Fair Value Measurements and Credit Concentration (Net Asset and Liability Measured on Recurring Basis Level 3 Observable Input Reconciliation Rollforward) (Details) (Level 3 [Member], USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012		Mar. 31, 2011
Reconciliation of net assets and liabilities
Balance at beginning of period	$ 41		$ 22
Total realized/unrealized gains (losses)
Included in earnings	18		1
Included in OCI	4	[1]	1	[1]
Purchases	0		2
Sales	0		(3)
Settlements	(6)		22
Transfers out of Level 3	(11)		12
Balance at end of period	46		57
Energy Commodities, Net [Member]
Reconciliation of net assets and liabilities
Balance at beginning of period	13		(3)
Total realized/unrealized gains (losses)
Included in earnings	18		1
Included in OCI	2	[1]	1	[1]
Purchases	0		2
Sales	0		(3)
Settlements	(6)		22
Transfers out of Level 3	(8)		12
Balance at end of period	19		32
Auction Rate Securities [Member]
Reconciliation of net assets and liabilities
Balance at beginning of period	24		25
Total realized/unrealized gains (losses)
Included in earnings	0		0
Included in OCI	0		0
Purchases	0		0
Sales	0		0
Settlements	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	4
Total realized/unrealized gains (losses)
Included in earnings	0
Included in OCI	2	[1]
Purchases	0
Sales	0
Settlements	0
Transfers out of Level 3	(3)
Balance at end of period	$ 3

[1] "Energy Commodities" and "Cross-Currency Swaps" are included in "Qualifying derivatives" on the Statements of Comprehensive Income.