Commitments and Contingencies, Environmental Contingencies - Unrecorded Unconditional Purchase Obligation (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014 Greenhouse Gas New Source Performance Standard for Modified and Reconstructed Power Plants	Sep. 30, 2014 Cross-State Air Pollution Rule MW	Apr. 30, 2014 Cross-State Air Pollution Rule Issue	Sep. 30, 2014 Capital Commitments Cross-State Air Pollution Rule
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%
Number of issues on which the D.C. Circuit overturned the CSAPR			2
Generating capacity (in MW)		700
Liability for estimated cost to comply with regulation				$ 7