Asset Retirement Obligations (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012
Asset Retirement Obligations [Abstract]
Damages sought in USDOE claim	$ 112
Estimated award range from USDOE claim, Low	65
Estimated award range from USDOE claim, High	75
Asset Retirement Obligation Increase related to Boardman plant	20
Asset Retirement Obligation Rate Recovery related to Trojan Plant	$ 4