Commitments and Contingencies, Environmental Contingencies - Unrecorded Unconditional Purchase Obligation (Details) $ in Millions	1 Months Ended	3 Months Ended
Feb. 29, 2016	Mar. 31, 2016 USD ($)
Implementation of the National Ambient Air Quality Standard for Sulfur Dioxide
Environmental Requirements [Abstract]
Number of phases under a consent decree which the EPA is requiring states to evaluate areas for attainment		3
Number of years unclassifiable areas will be monitored	3 years
Number of months in which the state would have to submit an implementation plan for the respective nonattainment areas		18 months
Number of years for the state to achieve the designated attainment standard		5 years
Capital Addition Purchase Commitments \| Regional Haze Rules
Environmental Requirements [Abstract]
Liability for estimated cost to comply with regulation		$ 600
Minimum \| Implementation of the National Ambient Air Quality Standard for Sulfur Dioxide
Environmental Requirements [Abstract]
Number of units which sulfur dioxide controls could be required		1

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Estimated undiscounted amount of the accrual required to comply with required regulation.

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Number of months in which the state would have to submit an implementation plan for the respective nonattaiment areas

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Number of phases under a consent decree which the EPA is requiring states to evaluate areas for attainment

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Number of units which sulfur dioxide controls could be required

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Number of years for the state to achieve the designated attainment standard

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Number of years unclassifiable areas will be monitored

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