Fair Value (Level 3 Reconciliation) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Fair Value Derivative Assets Liabilities Measured On Recurring Basis Unobservable Inputs [Abstract]
Balance at beginning of period	$ (396)	$ (148)
Included in earnings	(11)	5
Included in other comprehensive income	(17)	15
Included in regulatory (assets) liabilities	(1)	0
Settlements	22	8
Transfers of assets (liabilities) into Level 3		(28)
Transfers of (assets) liabilities out of Level 3	334	26
Balance at end of period	(69)	(122)
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	(12)	6
Interest Rate Derivatives
Fair Value Derivative Assets Liabilities Measured On Recurring Basis Unobservable Inputs [Abstract]
Balance at beginning of period	(412)	(128)
Included in earnings	0	(1)
Included in other comprehensive income	(17)	1
Included in regulatory (assets) liabilities	0	0
Settlements	23	6
Transfers of assets (liabilities) into Level 3		(28)
Transfers of (assets) liabilities out of Level 3	334	26
Balance at end of period	(72)	(124)
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	0
Cross Currency Swaps
Fair Value Derivative Assets Liabilities Measured On Recurring Basis Unobservable Inputs [Abstract]
Balance at beginning of period		(18)
Included in earnings		0
Included in other comprehensive income		14
Included in regulatory (assets) liabilities		0
Settlements		4
Transfers of assets (liabilities) into Level 3		0
Transfers of (assets) liabilities out of Level 3		0
Balance at end of period		0
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
Foreign Currency
Fair Value Derivative Assets Liabilities Measured On Recurring Basis Unobservable Inputs [Abstract]
Balance at beginning of period	73	51
Included in earnings	(1)	(2)
Included in other comprehensive income	0	0
Included in regulatory (assets) liabilities	0	0
Settlements	(1)	(1)
Transfers of assets (liabilities) into Level 3		0
Transfers of (assets) liabilities out of Level 3	0	0
Balance at end of period	71	48
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	(2)	(3)
Commodity & Other
Fair Value Derivative Assets Liabilities Measured On Recurring Basis Unobservable Inputs [Abstract]
Balance at beginning of period	(57)	(53)
Included in earnings	(10)	8
Included in other comprehensive income	0	0
Included in regulatory (assets) liabilities	(1)	0
Settlements	0	(1)
Transfers of assets (liabilities) into Level 3		0
Transfers of (assets) liabilities out of Level 3	0	0
Balance at end of period	(68)	(46)
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	$ (10)	$ 9