Fair Value (Level 3 Reconciliation) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance at beginning of period	$ (69)	$ (122)	$ (396)	$ (148)
Total gains (losses) (realized and unrealized):
Included in earnings	5	(13)	(7)	(8)
Included in other comprehensive income	13	(58)	83	(15)
Included in regulatory (assets) liabilities	11	7	10	7
Settlements	4	5	48	18
Transfers of assets (liabilities) into Level 3	(42)	(105)	0	(146)
Transfers of (assets) liabilities out of Level 3	29		213	6
Balance at end of period	(49)	(286)	(49)	(286)
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	(14)	(2)	(8)
Interest Rate [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance at beginning of period	(72)	(124)	(412)	(128)
Total gains (losses) (realized and unrealized):
Included in earnings	(4)	0	(4)	(1)
Included in other comprehensive income	13	(58)	83	(19)
Included in regulatory (assets) liabilities	0	0	0	0
Settlements	4	6	48	13
Transfers of assets (liabilities) into Level 3	(42)	(105)	0	(146)
Transfers of (assets) liabilities out of Level 3	38		222	0
Balance at end of period	(63)	(281)	(63)	(281)
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	0	0
Cross Currency [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance at beginning of period				(18)
Total gains (losses) (realized and unrealized):
Included in earnings				0
Included in other comprehensive income				4
Included in regulatory (assets) liabilities				0
Settlements				8
Transfers of assets (liabilities) into Level 3				0
Transfers of (assets) liabilities out of Level 3				6
Balance at end of period		0		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 derivatives [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance at beginning of period	71	48	73	51
Total gains (losses) (realized and unrealized):
Included in earnings	9	0	8	(2)
Included in other comprehensive income	0	0	0	0
Included in regulatory (assets) liabilities	0	0	0	0
Settlements	(1)	(1)	(2)	(2)
Transfers of assets (liabilities) into Level 3	0	0	0	0
Transfers of (assets) liabilities out of Level 3	(9)		(9)	0
Balance at end of period	70	47	70	47
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	11	(1)	7	(3)
Commodity [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance at beginning of period	(68)	(46)	(57)	(53)
Total gains (losses) (realized and unrealized):
Included in earnings	0	(13)	(11)	(5)
Included in other comprehensive income	0	0	0	0
Included in regulatory (assets) liabilities	11	7	10	7
Settlements	1	0	2	(1)
Transfers of assets (liabilities) into Level 3	0	0	0	0
Transfers of (assets) liabilities out of Level 3	0		0	0
Balance at end of period	(56)	(52)	(56)	(52)
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	$ (13)	$ (9)	$ (5)