Fair Value (Level 3 Reconciliation) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance at beginning of period	$ (4)	$ (341)
Total gains (losses) (realized and unrealized):
Included in earnings	137	70
Included in other comprehensive income - derivative activity	(156)	93
Included in other comprehensive income - foreign currency translation activity	(12)	(27)
Included in regulatory (assets) liabilities	16	2
Settlements	11	94
Transfers of assets (liabilities) into Level 3	10
Transfers of (assets) liabilities out of Level 3	3	105
Balance at end of period	5	(4)
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	131	64
Interest Rate
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance at beginning of period	(101)	(412)
Total gains (losses) (realized and unrealized):
Included in earnings	2	13
Included in other comprehensive income - derivative activity	(154)	93
Included in other comprehensive income - foreign currency translation activity	13	(4)
Included in regulatory (assets) liabilities	0	0
Settlements	30	100
Transfers of assets (liabilities) into Level 3	0
Transfers of (assets) liabilities out of Level 3	0	109
Balance at end of period	(210)	(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	2	10
Foreign currency derivatives
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance at beginning of period	93	72
Total gains (losses) (realized and unrealized):
Included in earnings	134	53
Included in other comprehensive income - derivative activity	(2)	0
Included in other comprehensive income - foreign currency translation activity	(25)	(23)
Included in regulatory (assets) liabilities	0	0
Settlements	(4)	(5)
Transfers of assets (liabilities) into Level 3	10
Transfers of (assets) liabilities out of Level 3	3	(4)
Balance at end of period	209	93
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	130	53
Commodity derivatives
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance at beginning of period	4	(1)
Total gains (losses) (realized and unrealized):
Included in earnings	1	4
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	16	2
Settlements	(15)	(1)
Transfers of assets (liabilities) into Level 3	0
Transfers of (assets) liabilities out of Level 3	0	0
Balance at end of period	6	4
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)	$ 1