Asset Retirement Obligations (Narrative) (Details) (USD $) In Millions, unless otherwise specified			9 Months Ended
	Sep. 30, 2013 Parent Company [Member]	Mar. 31, 2013 Parent Company [Member]	Sep. 30, 2013 Vermont Yankee [Member]
Guarantee To Satisfy NRC Requirements Following 2009 Review Of Financial Assurance Levels			$ 40
Vermont Yankee Decommissioning Trust Balance			584
NRC Minimum For Decommissioning Financial Assurance For License Termination			566
Increase in decommissioning liability	58		58
Reduction in decommissioning liability		$ 46.6