Fair Value (Level 3 Reconciliation) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance at beginning of period	$ 5	$ (4)
Total gains (losses) (realized and unrealized):
Included in earnings	25	25
Included in other comprehensive income — derivative activity	(35)	(65)
Included in other comprehensive income — foreign currency translation activity	5	(18)
Included in regulatory (assets) liabilities		(3)
Settlements	(1)	8
Transfers of assets (liabilities) into Level 3	(107)
Transfers of (assets) liabilities out of Level 3		71
Balance at the end of the period	(108)	14
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	24	25
Interest Rate [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance at beginning of period	(210)	(101)
Total gains (losses) (realized and unrealized):
Included in earnings	0	0
Included in other comprehensive income — derivative activity	(35)	(64)
Included in other comprehensive income — foreign currency translation activity	11	0
Included in regulatory (assets) liabilities		0
Settlements	6	8
Transfers of assets (liabilities) into Level 3	(74)
Transfers of (assets) liabilities out of Level 3		70
Balance at the end of the period	(302)	(87)
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
Foreign currency derivatives [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance at beginning of period	209	93
Total gains (losses) (realized and unrealized):
Included in earnings	22	26
Included in other comprehensive income — derivative activity	0	(1)
Included in other comprehensive income — foreign currency translation activity	(6)	(18)
Included in regulatory (assets) liabilities		0
Settlements	(2)	0
Transfers of assets (liabilities) into Level 3	0
Transfers of (assets) liabilities out of Level 3		1
Balance at the end of the period	223	101
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	21	26
Cross Currency [Domain]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance at beginning of period	0
Total gains (losses) (realized and unrealized):
Included in earnings	0
Included in other comprehensive income — derivative activity	0
Included in other comprehensive income — foreign currency translation activity	0
Settlements	0
Transfers of assets (liabilities) into Level 3	(33)
Balance at the end of the period	(33)
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
Commodity Contract [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance at beginning of period	6	4
Total gains (losses) (realized and unrealized):
Included in earnings	3	(1)
Included in other comprehensive income — derivative activity	0	0
Included in other comprehensive income — foreign currency translation activity	0	0
Included in regulatory (assets) liabilities		(3)
Settlements	(5)	0
Transfers of assets (liabilities) into Level 3	0
Transfers of (assets) liabilities out of Level 3		0
Balance at the end of the period	4	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	$ 3	$ (1)