Derivative Instruments (Details 2) (USD $) In Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2011		Sep. 30, 2010		Sep. 30, 2011		Sep. 30, 2010
Effect of derivative instruments on the statements of income and comprehensive income for instruments designated in cash flow hedging relationships and not in hedging relationships
Gain (Loss) Recognized in AOCL (Effective Portion)	$ 0		$ 2		$ 5		$ 7
Unrealized Gain (Loss) Recognized					0		(129)
Power Contracts
Effect of derivative instruments on the statements of income and comprehensive income for instruments designated in cash flow hedging relationships and not in hedging relationships
Gain (Loss) Recognized in AOCL (Effective Portion)	0		(1)		5		(3)
Power Contracts | Purchase Power Expense
Effect of derivative instruments on the statements of income and comprehensive income for instruments designated in cash flow hedging relationships and not in hedging relationships
Effective Gain (Loss) Reclassified to:	0	[1]	5	[1]	16	[1]	(2)	[1]
Unrealized Gain (Loss) Recognized	27		3		88		42
Additions/Change in value of existing contracts	(5)		(22)		(41)		(71)
Power Contracts | Revenue
Effect of derivative instruments on the statements of income and comprehensive income for instruments designated in cash flow hedging relationships and not in hedging relationships
Effective Gain (Loss) Reclassified to:	0	[1]	(7)	[1]	(12)	[1]	(11)	[1]
Unrealized Gain (Loss) Recognized	3				(1)
Additions/Change in value of existing contracts	(40)				(69)
Power Contracts | Fuel Expense
Effect of derivative instruments on the statements of income and comprehensive income for instruments designated in cash flow hedging relationships and not in hedging relationships
Effective Gain (Loss) Reclassified to:			0	[1]			0	[1]
Power Contracts | Other Operating Expense
Effect of derivative instruments on the statements of income and comprehensive income for instruments designated in cash flow hedging relationships and not in hedging relationships
Unrealized Gain (Loss) Recognized	(11)				(65)
Additions/Change in value of existing contracts	0				0
FTRs
Effect of derivative instruments on the statements of income and comprehensive income for instruments designated in cash flow hedging relationships and not in hedging relationships
Gain (Loss) Recognized in AOCL (Effective Portion)	0		0		0		0
FTRs | Purchase Power Expense
Effect of derivative instruments on the statements of income and comprehensive income for instruments designated in cash flow hedging relationships and not in hedging relationships
Effective Gain (Loss) Reclassified to:	0	[1]	0	[1]	0	[1]	0	[1]
Unrealized Gain (Loss) Recognized	0		0		0		0
Additions/Change in value of existing contracts	0		0		0		0
FTRs | Revenue
Effect of derivative instruments on the statements of income and comprehensive income for instruments designated in cash flow hedging relationships and not in hedging relationships
Effective Gain (Loss) Reclassified to:	0	[1]	0	[1]	0	[1]	0	[1]
Unrealized Gain (Loss) Recognized	0				0
Additions/Change in value of existing contracts	30				56
FTRs | Fuel Expense
Effect of derivative instruments on the statements of income and comprehensive income for instruments designated in cash flow hedging relationships and not in hedging relationships
Effective Gain (Loss) Reclassified to:			0	[1]			0	[1]
FTRs | Other Operating Expense
Effect of derivative instruments on the statements of income and comprehensive income for instruments designated in cash flow hedging relationships and not in hedging relationships
Unrealized Gain (Loss) Recognized	(15)				(1)
Additions/Change in value of existing contracts	(35)				(122)
Interest Rate Swap
Effect of derivative instruments on the statements of income and comprehensive income for instruments designated in cash flow hedging relationships and not in hedging relationships
Gain (Loss) Recognized in AOCL (Effective Portion)	0		0		0		0
Interest Rate Swap | Purchase Power Expense
Effect of derivative instruments on the statements of income and comprehensive income for instruments designated in cash flow hedging relationships and not in hedging relationships
Effective Gain (Loss) Reclassified to:	0	[1]	0	[1]	0	[1]	0	[1]
Unrealized Gain (Loss) Recognized	0		0		0		0
Additions/Change in value of existing contracts	0		0		0		0
Interest Rate Swap | Revenue
Effect of derivative instruments on the statements of income and comprehensive income for instruments designated in cash flow hedging relationships and not in hedging relationships
Effective Gain (Loss) Reclassified to:	0	[1]	0	[1]	0	[1]	0	[1]
Unrealized Gain (Loss) Recognized	0				0
Additions/Change in value of existing contracts	0				0
Interest Rate Swap | Fuel Expense
Effect of derivative instruments on the statements of income and comprehensive income for instruments designated in cash flow hedging relationships and not in hedging relationships
Effective Gain (Loss) Reclassified to:			0	[1]			0	[1]
Interest Rate Swap | Other Operating Expense
Effect of derivative instruments on the statements of income and comprehensive income for instruments designated in cash flow hedging relationships and not in hedging relationships
Unrealized Gain (Loss) Recognized	1				2
Additions/Change in value of existing contracts	0				0
NUGs | Regulatory Asset
Effect of derivative instruments on the statements of income and comprehensive income for instruments designated in cash flow hedging relationships and not in hedging relationships
Unrealized Gain (Loss) Recognized	89	[2]	146	[2]	325	[2]	405	[2]
Additions/Change in value of existing contracts	(53)	[2]	(63)	[2]
Realized Loss to Regulatory Assets:					(187)	[2]	(209)	[2]
NUGs | Derivative Instrument
Effect of derivative instruments on the statements of income and comprehensive income for instruments designated in cash flow hedging relationships and not in hedging relationships
Unrealized Gain (Loss) Recognized	(89)	[2]	(146)	[2]	(325)	[2]	(405)	[2]
Additions/Change in value of existing contracts	53	[2]	63	[2]	187	[2]	209	[2]
Other
Effect of derivative instruments on the statements of income and comprehensive income for instruments designated in cash flow hedging relationships and not in hedging relationships
Gain (Loss) Recognized in AOCL (Effective Portion)	0		3		0		10
Other | Purchase Power Expense
Effect of derivative instruments on the statements of income and comprehensive income for instruments designated in cash flow hedging relationships and not in hedging relationships
Effective Gain (Loss) Reclassified to:	0	[1]	0	[1]	0	[1]	0	[1]
Unrealized Gain (Loss) Recognized	0		0		0		0
Additions/Change in value of existing contracts	0		0		0		0
Other | Revenue
Effect of derivative instruments on the statements of income and comprehensive income for instruments designated in cash flow hedging relationships and not in hedging relationships
Effective Gain (Loss) Reclassified to:	0	[1]	0	[1]	0	[1]	0	[1]
Unrealized Gain (Loss) Recognized	0				0
Additions/Change in value of existing contracts	0				0
Other | Fuel Expense
Effect of derivative instruments on the statements of income and comprehensive income for instruments designated in cash flow hedging relationships and not in hedging relationships
Effective Gain (Loss) Reclassified to:			(4)	[1]			(11)	[1]
Other | Other Operating Expense
Effect of derivative instruments on the statements of income and comprehensive income for instruments designated in cash flow hedging relationships and not in hedging relationships
Unrealized Gain (Loss) Recognized	0				0
Additions/Change in value of existing contracts	0				0
Other | Regulatory Asset
Effect of derivative instruments on the statements of income and comprehensive income for instruments designated in cash flow hedging relationships and not in hedging relationships
Unrealized Gain (Loss) Recognized	3	[2]	0	[2]	0	[2]	0	[2]
Additions/Change in value of existing contracts	3	[2]	0	[2]
Realized Loss to Regulatory Assets:					14	[2]	9	[2]
Other | Derivative Instrument
Effect of derivative instruments on the statements of income and comprehensive income for instruments designated in cash flow hedging relationships and not in hedging relationships
Unrealized Gain (Loss) Recognized	(3)	[2]	0	[2]	0	[2]	0	[2]
Additions/Change in value of existing contracts	(3)	[2]	0	[2]	(14)	[2]	(9)	[2]
Purchase Power Expense
Effect of derivative instruments on the statements of income and comprehensive income for instruments designated in cash flow hedging relationships and not in hedging relationships
Effective Gain (Loss) Reclassified to:	0	[1]	5	[1]	16	[1]	(2)	[1]
Unrealized Gain (Loss) Recognized	27		3		88		42
Additions/Change in value of existing contracts	(5)		(22)		(41)		(71)
Revenue
Effect of derivative instruments on the statements of income and comprehensive income for instruments designated in cash flow hedging relationships and not in hedging relationships
Effective Gain (Loss) Reclassified to:	0	[1]	(7)	[1]	(12)	[1]	(11)	[1]
Unrealized Gain (Loss) Recognized	3				(1)
Additions/Change in value of existing contracts	(10)				(13)
Fuel Expense
Effect of derivative instruments on the statements of income and comprehensive income for instruments designated in cash flow hedging relationships and not in hedging relationships
Effective Gain (Loss) Reclassified to:			(4)	[1]			(11)	[1]
Other Operating Expense
Effect of derivative instruments on the statements of income and comprehensive income for instruments designated in cash flow hedging relationships and not in hedging relationships
Unrealized Gain (Loss) Recognized	(25)				(64)
Additions/Change in value of existing contracts	(35)				(122)
Regulatory Asset
Effect of derivative instruments on the statements of income and comprehensive income for instruments designated in cash flow hedging relationships and not in hedging relationships
Unrealized Gain (Loss) Recognized	92	[2]	146	[2]	325	[2]	405	[2]
Additions/Change in value of existing contracts	(50)	[2]	(63)	[2]
Realized Loss to Regulatory Assets:					(173)	[2]	(200)	[2]
Derivative Instrument
Effect of derivative instruments on the statements of income and comprehensive income for instruments designated in cash flow hedging relationships and not in hedging relationships
Unrealized Gain (Loss) Recognized	(92)	[2]	(146)	[2]	(325)	[2]	(405)	[2]
Additions/Change in value of existing contracts	$ 50	[2]	$ 63	[2]	$ 173	[2]	$ 200	[2]

[1] The ineffective portion was immaterial.

[2] Changes in the fair value of certain contracts are deferred for future recovery from (or refund to) customers.