Fair Value (Level 3 Reconciliation) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Fair Value Derivative Assets Liabilities Measured On Recurring Basis Unobservable Inputs [Abstract]
Balance at beginning of period	$ (148)	$ 49
Included in earnings	12	(43)
Included in other comprehensive income	(26)	(50)
Included in regulatory (assets) liabilities	9	8
Settlements	36	2
Transfers of assets (liabilities) into Level 3	(285)	(117)
Transfers of (assets) liabilities out of Level 3	6	3
Balance at end of period	(396)	(148)
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	(44)
Interest Rate Derivatives
Fair Value Derivative Assets Liabilities Measured On Recurring Basis Unobservable Inputs [Abstract]
Balance at beginning of period	(128)	(1)
Included in earnings	(2)	0
Included in other comprehensive income	(29)	(13)
Included in regulatory (assets) liabilities	0	0
Settlements	26	0
Transfers of assets (liabilities) into Level 3	(285)	(117)
Transfers of (assets) liabilities out of Level 3	6	3
Balance at end of period	(412)	(128)
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
Cross Currency Swaps
Fair Value Derivative Assets Liabilities Measured On Recurring Basis Unobservable Inputs [Abstract]
Balance at beginning of period	(18)	10
Included in earnings	0	(4)
Included in other comprehensive income	3	(37)
Included in regulatory (assets) liabilities	0	0
Settlements	15	13
Transfers of assets (liabilities) into Level 3	0	0
Transfers of (assets) liabilities out of Level 3	0	0
Balance at end of period	0	(18)
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)
Foreign Currency Options and Forwards
Fair Value Derivative Assets Liabilities Measured On Recurring Basis Unobservable Inputs [Abstract]
Balance at beginning of period	51	22
Included in earnings	25	32
Included in other comprehensive income	0	0
Included in regulatory (assets) liabilities	0	0
Settlements	(3)	(3)
Transfers of assets (liabilities) into Level 3	0	0
Transfers of (assets) liabilities out of Level 3	0	0
Balance at end of period	73	51
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	22	29
Commodity & Other
Fair Value Derivative Assets Liabilities Measured On Recurring Basis Unobservable Inputs [Abstract]
Balance at beginning of period	(53)	18
Included in earnings	(11)	(71)
Included in other comprehensive income	0	0
Included in regulatory (assets) liabilities	9	8
Settlements	(2)	(8)
Transfers of assets (liabilities) into Level 3	0	0
Transfers of (assets) liabilities out of Level 3	0	0
Balance at end of period	(57)	(53)
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	$ (3)	$ (71)