Fair Value (Level 3 Reconciliation) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Fair Value Derivative Assets Liabilities Measured On Recurring Basis Unobservable Inputs [Abstract]
Balance at beginning of period	$ (286)	$ 10	$ (148)	$ 49
Included in earnings	29	(43)	21	(34)
Included in other comprehensive income	(29)	(73)	(22)	(37)
Included in regulatory (assets) liabilities	2	(3)	9	3
Settlements	7	(1)	23	(3)
Transfers of assets (liabilities) into Level 3	0	(101)	(159)	(189)
Transfers of (assets) liabilities out of Level 3	2	2	1	2
Balance at end of period	(275)	(209)	(275)	(209)
Total gains/(losses) for the period included in earnings attributable to the change in unrealized gains/(losses) relating to assets and liabilities held at the end of the period	30	(52)	22	(40)
Interest Rate Derivatives
Fair Value Derivative Assets Liabilities Measured On Recurring Basis Unobservable Inputs [Abstract]
Balance at beginning of period	(281)	(60)	(128)	(1)
Included in earnings	(1)	0	(1)	0
Included in other comprehensive income	(29)	(36)	(30)	(3)
Included in regulatory (assets) liabilities	0	0	0	0
Settlements	12	4	19	0
Transfers of assets (liabilities) into Level 3	0	(101)	(159)	(189)
Transfers of (assets) liabilities out of Level 3	2	2	2	2
Balance at end of period	(297)	(191)	(297)	(191)
Total gains/(losses) for the period included in earnings attributable to the change in unrealized gains/(losses) relating to assets and liabilities held at the end of the period	(1)	0	(1)	0
Cross Currency Swaps
Fair Value Derivative Assets Liabilities Measured On Recurring Basis Unobservable Inputs [Abstract]
Balance at beginning of period	0	15	(18)	10
Included in earnings	0	(3)	0	(5)
Included in other comprehensive income	0	(37)	8	(34)
Included in regulatory (assets) liabilities	0	0	0	0
Settlements	0	4	11	8
Transfers of assets (liabilities) into Level 3	0	0	0	0
Transfers of (assets) liabilities out of Level 3	0	0	(1)	0
Balance at end of period	0	(21)	0	(21)
Total gains/(losses) for the period included in earnings attributable to the change in unrealized gains/(losses) relating to assets and liabilities held at the end of the period	0	(2)	0	(2)
Foreign Currency
Fair Value Derivative Assets Liabilities Measured On Recurring Basis Unobservable Inputs [Abstract]
Balance at beginning of period	47	38	51	22
Included in earnings	14	4	12	21
Included in other comprehensive income	0	0	0	0
Included in regulatory (assets) liabilities	0	0	0	0
Settlements	(1)	(1)	(3)	(2)
Transfers of assets (liabilities) into Level 3	0	0	0	0
Transfers of (assets) liabilities out of Level 3	0	0	0	0
Balance at end of period	60	41	60	41
Total gains/(losses) for the period included in earnings attributable to the change in unrealized gains/(losses) relating to assets and liabilities held at the end of the period	13	2	10	18
Commodity & Other
Fair Value Derivative Assets Liabilities Measured On Recurring Basis Unobservable Inputs [Abstract]
Balance at beginning of period	(52)	17	(53)	18
Included in earnings	16	(44)	10	(50)
Included in other comprehensive income	0	0	0	0
Included in regulatory (assets) liabilities	2	(3)	9	3
Settlements	(4)	(8)	(4)	(9)
Transfers of assets (liabilities) into Level 3	0	0	0	0
Transfers of (assets) liabilities out of Level 3	0	0	0	0
Balance at end of period	(38)	(38)	(38)	(38)
Total gains/(losses) for the period included in earnings attributable to the change in unrealized gains/(losses) relating to assets and liabilities held at the end of the period	$ 18	$ (52)	$ 13	$ (56)