Commitments and Contingencies, Environmental Contingencies (Details) (USD $) In Millions, unless otherwise specified	1 Months Ended	12 Months Ended
	Apr. 30, 2012 MW	Dec. 31, 2014	Jun. 30, 2014	Apr. 30, 2014 Issue
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
Generating capacity (in MW)		700
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
Regional Haze Rules
Environmental Requirements [Abstract]
Number of years to comply with proposed regulation		5 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
Proposed level of air quality concentrations (in parts per million)		0.070
Lowest proposed level of air quality concentrations that the EPA is taking comment on (in parts per million)		0.060
Capital Commitments | Cross-State Air Pollution Rule
Environmental Requirements [Abstract]
Liability for estimated cost to comply with regulation		7
Capital Commitments | Regional Haze Rules
Environmental Requirements [Abstract]
Liability for estimated cost to comply with regulation		600
Estimated annual operating cost to comply with proposed regulation		10.4
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