Fair Value Measurements and Credit Concentration (Net Asset and Liability Measured on Recurring Basis Level 3 Observable Input Reconciliation Rollforward) (Details) (USD $) In Millions	3 Months Ended				6 Months Ended				3 Months Ended				6 Months Ended
	Jun. 30, 2011		Jun. 30, 2010		Jun. 30, 2011		Jun. 30, 2010		Jun. 30, 2011 Energy Commodities, Net [Member]		Jun. 30, 2010 Energy Commodities, Net [Member]		Jun. 30, 2011 Energy Commodities, Net [Member]		Jun. 30, 2010 Energy Commodities, Net [Member]		Jun. 30, 2011 Auction Rate Securities [Member]	Mar. 31, 2011 Auction Rate Securities [Member]	Dec. 31, 2010 Auction Rate Securities [Member]	Jun. 30, 2010 Auction Rate Securities [Member]	Mar. 31, 2010 Auction Rate Securities [Member]	Dec. 31, 2009 Auction Rate Securities [Member]
Reconciliation of net assets and liabilities
Balance at beginning of period	$ 57		$ 76		$ 22		$ 132		$ 32		$ 51		$ (3)		$ 107		$ 25	$ 25	$ 25	$ 25	$ 25	$ 25
Total realized/unrealized gains (losses)
Included in earnings	(5)		(7)		(4)		(68)		(5)		(7)		(4)		(68)
Included in OCI	3	[1]	5	[1]	4	[1]	8	[1]	3	[1]	5	[1]	4	[1]	8	[1]
Purchases, sales, issuances and settlements, net			(4)	[2]			1	[2]			(4)	[2]			1	[2]
Purchases	0				2				0				2
Sales	(1)				(4)				(1)				(4)
Settlements	3				25				3				25
Transfers into Level 3			0				(2)				0				(2)
Transfers out of Level 3	(6)		3		6		2		(6)		3		6		2
Balance at end of period	$ 51		$ 73		$ 51		$ 73		$ 26		$ 48		$ 26		$ 48		$ 25	$ 25	$ 25	$ 25	$ 25	$ 25

[1] Included in "Qualifying derivatives" on the Statements of Comprehensive Income.

[2] Accounting guidance effective January 1, 2011 requires purchase, sale, issuance and settlement transactions within Level 3 to be presented on a gross basis. The transactions in 2010 are reported on a combined basis.