Balance Sheet Components (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011	Dec. 31, 2010
Valuation and Qualifying Accounts Disclosure [Line Items]
Allowance for Doubtful Accounts Receivable, Current	$ 6	$ 5	$ 6	$ 5
Finite-Lived Intangible Assets, Accumulated Amortization	158		153
Amortization of Intangible Assets	5	5
Sale Leaseback Transaction, Construction Cost	10
Asset Retirement Obligation Increase related to Boardman plant		23	20
Credit Facilities - $370 million revolver	370
Portion of $370 million credit facility scheduled to terminate in July 2012	10
Portion of $370 million credit facility scheduled to terminate in July 2013	360
Credit Facilities - $300 million revolver	300
Debt Instrument, Covenant Description	0.650
Ratio of Indebtedness to Net Capital	0.506
Authorized Short-Term Debt	700
Borrowings	0		0
Commercial Paper	0		30
Letters of Credit Issued	137		124
Line of Credit Facility, Remaining Borrowing Capacity	$ 533