Fair Value Measurements and Credit Concentration (Net Asset and Liability Measured on Recurring Basis Level 3 Observable Input Reconciliation Rollforward) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010
Reconciliation of net assets and liabilities
Balance at beginning of period	$ 22		$ 132
Total realized/unrealized gains (losses)
Included in earnings	(65)		(137)
Included in OCI	(12)	[1]	11	[1]
Net purchases, sales, issuances and settlements			(16)	[2]
Purchases	1
Sales	(3)
Settlements	20
Transfers into Level 3	4		(15)
Transfers out of Level 3	74		47
Balance at end of period	41		22
Energy Commodities, Net [Member]
Reconciliation of net assets and liabilities
Balance at beginning of period	(3)		107
Total realized/unrealized gains (losses)
Included in earnings	(65)		(137)
Included in OCI	(1)	[1]	11	[1]
Net purchases, sales, issuances and settlements			(16)	[2]
Purchases	1
Sales	(3)
Settlements	20
Transfers into Level 3	(10)		(15)
Transfers out of Level 3	74		47
Balance at end of period	13		(3)
Auction Rate Securities [Member]
Reconciliation of net assets and liabilities
Balance at beginning of period	25		25
Total realized/unrealized gains (losses)
Included in earnings	0		0
Included in OCI	(1)	[1]	0
Net purchases, sales, issuances and settlements			0
Purchases	0
Sales	0
Settlements	0
Transfers into Level 3	0		0
Transfers out of Level 3	0		0
Balance at end of period	24		25
Cross Currency Swaps [Member]
Reconciliation of net assets and liabilities
Balance at beginning of period	0		0
Total realized/unrealized gains (losses)
Included in earnings	0		0
Included in OCI	(10)	[1]	0
Net purchases, sales, issuances and settlements			0
Purchases	0
Sales	0
Settlements	0
Transfers into Level 3	14		0
Transfers out of Level 3	0		0
Balance at end of period	$ 4		$ 0

[1] "Energy Commodities" and "Cross-Currency Swaps" are included in "Qualifying derivatives" and "Auction Rate Securities" are included in "Available-for-sale securities" 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 net basis.