Commitments and Contingencies Commitments and Contingencies, Environmental Contingencies - Unrecorded Unconditional Purchase Obligation (Details) (USD $) In Millions, unless otherwise specified	1 Months Ended
	Apr. 30, 2012 MW	Jun. 30, 2014	Apr. 30, 2014 Issue	Dec. 31, 2014 Parts-per-million
Greenhouse Gas New Source Performance Standard for Modified and Reconstructed Power Plants
Environmental Requirements [Abstract]
Percentage of a comparable new plant's capital cost which would have to be exceeded to consider a project as a reconstruction under the proposed GHG NSPS for Modified and Reconstructed Power Plants (in hundredths)		50.00%
Cross-State Air Pollution Rule
Environmental Requirements [Abstract]
Number of issues on which the D.C. Circuit overturned the CSAPR			2
Electric Generating Unit Mercury And Air Toxics Standards Rule
Environmental Requirements [Abstract]
Generating capacity (in MW)	25
Number of years before affected facilities must demonstrate compliance, low end of range	3 years
Number of years before affected facilities must demonstrate compliance, high end of range	4 years
National Ambient Air Quality Standards for Ozone
Environmental Requirements [Abstract]
Number of hours the NAAQS for Ozone is based upon (in hours)				8
Current level of air quality concentrations (in parts per million)				0.075
Lowest proposed level of air quality concentrations that the EPA is taking comment on (in parts per million)				0.060
Capital Commitments | Federal Clean Water Act Section 316(b)
Environmental Requirements [Abstract]
Liability for estimated cost to comply with regulation				4.0
Capital Commitments | Industrial Boiler Maximum Achievable Control Technology Rules
Environmental Requirements [Abstract]
Liability for estimated cost to comply with regulation				21.0
Minimum | National Ambient Air Quality Standards for Ozone
Environmental Requirements [Abstract]
Proposed level of air quality concentrations (in parts per million)				0.065
Maximum | National Ambient Air Quality Standards for Ozone
Environmental Requirements [Abstract]
Proposed level of air quality concentrations (in parts per million)				0.070