Commitments and Guarantees Commitments and Guarantees (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 1985
Unrecorded Unconditional Purchase Obligation [Line Items]
percentage of output	25.00%
Operating Leases, Rent Expense	$ 9	$ 9	$ 7
Long-term Contract for Purchase of Electric Power, Estimated Annual Cost	13
Future Minimum Sublease Rentals, Sale Leaseback Transactions, within One Year	3
Future Minimum Sublease Rentals, Sale Leaseback Transactions, within Two Years	2
Future Minimum Sublease Rentals, Sale Leaseback Transactions, within Five Years	1
Operating Leases, Rent Expense, Sublease Rentals	3	3	3
Ownership interest in Boardman sold				15.00%
ownership interest in Pacific Northwest Intertie sold				10.714%
maximum potential liability under power and transmission agreements	74
Future Minimum Sublease Rentals, Sale Leaseback Transactions, within Three Years	2
Future Minimum Sublease Rentals, Sale Leaseback Transactions, within Four Years	$ 2