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				9 Months Ended
	Sep. 30, 2011		Sep. 30, 2010		Sep. 30, 2011		Sep. 30, 2010
Reconciliation of net assets and liabilities
Balance at beginning of period	$ 51		$ 73		$ 22		$ 132
Total realized/unrealized gains (losses)
Included in earnings	6		(58)		2		(126)
Included in OCI	1	[1]	4	[2]	5	[1]	12	[2]
Purchases, sales, issuances and settlements, net			(13)	[3]			(12)	[3]
Purchases					2
Sales					(4)
Settlements	(2)				23
Transfers into Level 3			(13)		13		(15)
Transfers out of Level 3	(5)		46		1		48
Balance at end of period	64		39		64		39
Energy Commodities, Net [Member]
Reconciliation of net assets and liabilities
Balance at beginning of period	26		48		(3)		107
Total realized/unrealized gains (losses)
Included in earnings	6		(58)		2		(126)
Included in OCI	2	[1]	4	[2]	6	[1]	12	[2]
Purchases, sales, issuances and settlements, net			(13)	[3]			(12)	[3]
Purchases					2
Sales					(4)
Issuances					23
Settlements	(2)
Transfers into Level 3	(1)		(13)		(1)		(15)
Transfers out of Level 3	(5)		46		1		48
Balance at end of period	26		14		26		14
Auction Rate Securities [Member]
Reconciliation of net assets and liabilities
Balance at beginning of period	25		25		25		25
Total realized/unrealized gains (losses)
Included in OCI	(1)	[1]	0		(1)	[1]	0
Balance at end of period	24		25		24		25
Cross Currency Swaps [Member]
Reconciliation of net assets and liabilities
Balance at beginning of period	0				0
Total realized/unrealized gains (losses)
Transfers into Level 3	14				14
Balance at end of period	$ 14				$ 14

[1] "Energy Commodities" are included in "Qualifying derivatives" and "Auction Rate Securities" are included in "Available-for-sale securities" on the Statements of Comprehensive Income.

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

[3] 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.