Commitments and Contingencies, Environmental Contingencies (Details) $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($)	Oct. 30, 2015 Period
Cross-State Air Pollution Rule
Unrecorded Unconditional Purchase Obligation [Line Items]
Proposed percent reduction related to the ozone season emission budget for Nitrogen Oxide	14.00%
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 months in which the state would have to submit an implementation plan for the respective nonattaiment areas	18 months
Number of years for the state to achieve the designated attainment standard	5 years
National Ambient Air Quality Standards for Ozone
Environmental Requirements [Abstract]
Number of hours measured for standard | Period		8
Current level of air quality concentrations (in parts per billion)		75
Proposed level of air quality concentrations (in parts per billion)		70
Capital 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