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Supplemental Oil and Gas Disclosures - Schedule of Changes in Standardized Measure (Details) (USD $)
In Millions, unless otherwise specified |
12 Months Ended | ||
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Dec. 31, 2014
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Dec. 31, 2013
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Dec. 31, 2012
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| Changes in Standardized Measure | |||
| Changes in Standardized Measure Standardized measure, beginning of year | $ 1,674.6us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves | $ 1,846.4us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves | $ 2,006.4us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves |
| Sales and transfers of oil and gas produced, net of production costs | (650.9)us-gaap_SalesAndTransfersOfOilAndGasProducedNetOfProductionCosts | (686.1)us-gaap_SalesAndTransfersOfOilAndGasProducedNetOfProductionCosts | (620.4)us-gaap_SalesAndTransfersOfOilAndGasProducedNetOfProductionCosts |
| Net changes in price, net of future production costs | (278.6)us-gaap_NetIncreaseDecreaseInSalesAndTransferPricesAndProductionCosts | (65.2)us-gaap_NetIncreaseDecreaseInSalesAndTransferPricesAndProductionCosts | (224.3)us-gaap_NetIncreaseDecreaseInSalesAndTransferPricesAndProductionCosts |
| Extensions and discoveries, net of future production and development costs | 309.6us-gaap_ExtensionsDiscoveriesAdditionsAndImprovedRecoveryLessRelatedCosts | 393.8us-gaap_ExtensionsDiscoveriesAdditionsAndImprovedRecoveryLessRelatedCosts | 181.9us-gaap_ExtensionsDiscoveriesAdditionsAndImprovedRecoveryLessRelatedCosts |
| Changes in estimated future development costs | (56.4)us-gaap_IncreaseDecreaseInEstimatedFutureDevelopmentCosts | (91.1)us-gaap_IncreaseDecreaseInEstimatedFutureDevelopmentCosts | (103.3)us-gaap_IncreaseDecreaseInEstimatedFutureDevelopmentCosts |
| Previously estimated development costs incurred | 263.1us-gaap_PreviouslyEstimatedDevelopmentCostsIncurredDuringPeriod | 262.1us-gaap_PreviouslyEstimatedDevelopmentCostsIncurredDuringPeriod | 332.9us-gaap_PreviouslyEstimatedDevelopmentCostsIncurredDuringPeriod |
| Revisions of quantity estimates | 118.6us-gaap_RevisionsOfPreviousQuantityEstimates | (91.6)us-gaap_RevisionsOfPreviousQuantityEstimates | (128.1)us-gaap_RevisionsOfPreviousQuantityEstimates |
| Accretion of discount | 180.6us-gaap_AccretionOfDiscount | 202.2us-gaap_AccretionOfDiscount | 231.1us-gaap_AccretionOfDiscount |
| Net change in income taxes | (11.4)us-gaap_IncreaseDecreaseInFutureIncomeTaxExpenseEstimatesOnFutureCashFlowsRelatedToProvedOilAndGasReserves | 56.6us-gaap_IncreaseDecreaseInFutureIncomeTaxExpenseEstimatesOnFutureCashFlowsRelatedToProvedOilAndGasReserves | 99.7us-gaap_IncreaseDecreaseInFutureIncomeTaxExpenseEstimatesOnFutureCashFlowsRelatedToProvedOilAndGasReserves |
| Purchases of reserves in-place | 86.7us-gaap_IncreaseDueToPurchasesOfMineralsInPlace | 79.6us-gaap_IncreaseDueToPurchasesOfMineralsInPlace | 270.2us-gaap_IncreaseDueToPurchasesOfMineralsInPlace |
| Sales of reserves in-place | (53.1)us-gaap_DecreaseDueToSalesOfMineralsInPlace | (16.1)us-gaap_DecreaseDueToSalesOfMineralsInPlace | |
| Changes in production rates due to timing and other | 66.9us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowOfProvedOilAndGasReservesOther | (179.0)us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowOfProvedOilAndGasReservesOther | (183.6)us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowOfProvedOilAndGasReservesOther |
| Net increase (decrease) in standardized measure | 28.2us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowOfProvedOilAndGasReservesPeriodIncreaseDecrease | (171.8)us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowOfProvedOilAndGasReservesPeriodIncreaseDecrease | (160.0)us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowOfProvedOilAndGasReservesPeriodIncreaseDecrease |
| Changes in Standardized measure, end of year | $ 1,702.8us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves | $ 1,674.6us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves | $ 1,846.4us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves |
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- Definition
Amount of increase (decrease) in standardized measure of discounted future net cash flow as a result of passage of time. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
Amount of decrease in standardized measure of discounted future net cash flow as a result of sales of minerals in place. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
Amount of increase (decrease) in standardized measure of discounted future net cash flow as a result of extensions, discoveries and improved recovery of proved oil and gas reserves. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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| X | ||||||||||
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- Definition
Amount of increase (decrease) in standardized measure of discounted future net cash flow as a result of change in estimated future development costs. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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| X | ||||||||||
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- Definition
Amount of increase (decrease) in standardized measure of discounted future net cash flow as a result of change in the estimated future income tax on future pretax net cash flows related to the entity's proved oil and gas reserves. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
Amount of increase in standardized measure of discounted future net cash flow as a result of purchases of minerals in place. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
Amount of increase (decrease) in standardized measure of discounted future net cash flow as a result of change in sales and transfer prices and in production (lifting) costs related to future production. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
Amount of (increase) decrease in standardized measure of discounted future net cash flow as a result of previously estimated development costs incurred. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Details
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- Definition
Amount of increase (decrease) in standardized measure of discounted future net cash flow as a result of revisions of estimated quantity of oil and gas in proved reserves. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
Amount of (increase) decrease in standardized measure of discounted future net cash flow as a result of sales and transfers of oil and gas produced. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
Amount of increase (decrease) in standardized measure of discounted future net cash flow as a result of changes from other sources. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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| X | ||||||||||
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- Definition
Amount of increase (decrease) in standardized measure of discounted future net cash flow relating to proved oil and gas reserves. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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| X | ||||||||||
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- Definition
Amount of discounted future accumulated cash inflow relating to proved oil and gas reserves. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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