Fair Value Measurements and Credit Concentration (Net Asset and Liability Measured on Recurring Basis Level 3 Unobservable Inputs Reconciliation Rollforward) (Details) (Recurring [Member], Level 3 [Member], USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014
Reconciliation of net assets and liabilities
Balance at beginning of period	$ 122		$ 43
Total realized/unrealized gains (losses)
Included in earnings	(17)		(135)
Included in OCI	6	[1]	(1)	[1]
Sales	0		(3)
Settlements	30		128
Transfers into Level 3	4		0
Transfers out of Level 3	(6)		1
Balance at end of period	139		33
Energy Commodities, Net [Member]
Reconciliation of net assets and liabilities
Balance at beginning of period	111		24
Total realized/unrealized gains (losses)
Included in earnings	(17)		(135)
Included in OCI	0		0
Sales	0		0
Settlements	30		128
Transfers into Level 3	4		0
Transfers out of Level 3	1		0
Balance at end of period	129		17
Auction Rate Securities [Member]
Reconciliation of net assets and liabilities
Balance at beginning of period	10		19
Total realized/unrealized gains (losses)
Included in earnings	0		0
Included in OCI	0		0
Sales	0		(3)
Settlements	0		0
Transfers into Level 3	0		0
Transfers out of Level 3	0		0
Balance at end of period	10		16
Cross Currency Swaps [Member]
Reconciliation of net assets and liabilities
Balance at beginning of period	1		0
Total realized/unrealized gains (losses)
Included in earnings	0		0
Included in OCI	6	[1]	(1)	[1]
Sales	0		0
Settlements	0		0
Transfers into Level 3	0		0
Transfers out of Level 3	(7)		1
Balance at end of period	$ 0		$ 0

[1] "Energy Commodities, net" 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.