Derivative Instruments (Income Statement Disclosure) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2014		Jun. 30, 2013		Jun. 30, 2014		Jun. 30, 2013
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	$ (7)		$ 27		$ 7		$ 61
Effect of Cash Flow Hedges on Results of Operations [Abstract]
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net	(10)		61		(39)		153
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net [Abstract]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	(167)		14		(465)		(57)
Gains (losses) on commodity contracts, recorded as regulatory assets and or liabilities on the balance sheet due to regulatory treatment	11		(149)		147		(5)
Commodity Contract [Member] | Gains (losses) included in operating revenues [Member]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net [Abstract]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	(153)		15		(425)		(27)
Commodity Contract [Member] | Gains (losses) included in fuel, purchased power and interchange [Member]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net [Abstract]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	0		8		(4)		11
Interest Rate Contract [Member]
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	16	[1]	15	[1]	32	[1]	30	[1]
Effect of Cash Flow Hedges on Results of Operations [Abstract]
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net	(27)		65		(54)		165
Interest Rate Contract [Member] | Gain Loss Included In Interest Expense Member
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net [Abstract]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	(8)		11		(35)		11
Foreign Exchange Contract [Member]
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	(23)	[2]	12	[2]	(25)	[3]	31	[3]
Effect of Cash Flow Hedges on Results of Operations [Abstract]
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net	17		(4)		15		(12)
Foreign Exchange Contract [Member] | Gains (losses) included in Other - net [Member]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net [Abstract]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	(6)		(20)		(1)		(52)
Fair Value Hedging [Member]
Derivative [Line Items]
Increase (Decrease) in Fair Value of Hedged Item in Interest Rate Fair Value Hedge	15		(48)		19		(57)
Cash Flow Hedging [Member] | Currency Swap [Member] | Gains (losses) included in interest expense [Member]
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	$ 1		$ 1		$ 2		$ 2

[1] Included in interest expense.

[2] Loss of approximately $1 million is included in interest expense and the balance is included in other - net.

[3] Loss of approximately $2 million is included in interest expense and the balance is included in other - net.