Commitments and Contingencies, Environmental Contingencies - Unrecorded Unconditional Purchase Obligation (Details) $ in Millions	1 Months Ended	9 Months Ended
	Sep. 30, 2016 USD ($)	Sep. 30, 2016 USD ($)
Cross-State Air Pollution Rule (CSAPR) [Member]
Environmental Requirements [Abstract]
Adopted Reduction Related to the Ozone Season Emission Budget for NOx	22.00%
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
Capital Addition Purchase Commitments | Regional Haze Rules
Environmental Requirements [Abstract]
Liability for estimated cost to comply with regulation	$ 600	$ 600