Commitments and Contingencies, Environmental Contingencies (Details) $ in Millions	1 Months Ended	12 Months Ended
	Sep. 30, 2016	Dec. 31, 2016 USD ($)	Dec. 31, 2015 Period
Cross-State Air Pollution Rule (CSAPR)
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
National Ambient Air Quality Standards for Ozone
Environmental Requirements [Abstract]
Number of Hours Measured for Standard | Period			8
Former Level of Air Quality Concentrations (in parts per billion)			75
Revised Level of Air Quality Concentrations (in parts per billion)		70	70
Harrington Units 1 and 2 | Implementation of the National Ambient Air Quality Standard for Sulfur Dioxide
Environmental Requirements [Abstract]
Number of Years Unclassifiable Areas Will Be Monitored		3 years
Harrington Units 1 and 2 | Capital Commitments | Regional Haze Rules
Environmental Requirements [Abstract]
Liability for Estimated Cost to Comply with Regulation		$ 400
Tolk Units 1 and 2 | Capital Commitments | Regional Haze Rules
Environmental Requirements [Abstract]
Liability for Estimated Cost to Comply with Regulation		$ 600