Fair Value of Financial Instruments (Details 3) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2012		Sep. 30, 2011
Reconciliation of the beginning and ending balances for financial instruments that are recognized at fair value in the consolidated financial statements
Balance at the beginning of the period	$ 223		$ 24		$ 57		$ 20
Total gains and losses (realized/unrealized):
Included in earnings			0				19
Fair Value, Assets and Liabilities Measured on Recurring Basis, Gain (Loss) Included in Earnings	(9)				(3)
Included in OCI	2		(1)		4		0
Included in nuclear decommissioning obligations	3		(8)		3		(7)
Purchases	(109)		(2)		0		7
Transfer into Level 3			13	[1]			(17)	[1]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3	(31)	[1]			4	[1]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3	(20)	[1]			(6)	[1]
Transfer out of Level 3			8	[1]			12	[1]
Balance at the end of the period	59		34		59		34
The amount of the total gains for the period included in earnings attributable to the change in unrealized gains relating to assets still held at the end of the period	(5)		(1)		1		6
Debt Securities
Reconciliation of the beginning and ending balances for financial instruments that are recognized at fair value in the consolidated financial statements
Balance at the beginning of the period	9		9		7		8
Total gains and losses (realized/unrealized):
Included in earnings			0				0
Fair Value, Assets and Liabilities Measured on Recurring Basis, Gain (Loss) Included in Earnings	0				0
Included in OCI	2		(1)		4		0
Included in nuclear decommissioning obligations	0		0		0		0
Purchases	0		0		0		0
Transfer into Level 3			0	[1]			0	[1]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3	0				0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3	0				0
Transfer out of Level 3			0	[1]			0	[1]
Balance at the end of the period	11		8		11		8
The amount of the total gains for the period included in earnings attributable to the change in unrealized gains relating to assets still held at the end of the period	0		0		0		0
Trust Fund Investment [Member]
Reconciliation of the beginning and ending balances for financial instruments that are recognized at fair value in the consolidated financial statements
Balance at the beginning of the period	43		41		42		39
Total gains and losses (realized/unrealized):
Included in earnings			0				0
Fair Value, Assets and Liabilities Measured on Recurring Basis, Gain (Loss) Included in Earnings	0				0
Included in OCI	0		0		0		0
Included in nuclear decommissioning obligations	3		(8)		3		(7)
Purchases	0		0		1		1
Transfer into Level 3			0	[1]			0	[1]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3	0				0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3	0				0
Transfer out of Level 3			0	[1]			0	[1]
Balance at the end of the period	46		33		46		33
The amount of the total gains for the period included in earnings attributable to the change in unrealized gains relating to assets still held at the end of the period	0		0		0		0
Derivatives
Reconciliation of the beginning and ending balances for financial instruments that are recognized at fair value in the consolidated financial statements
Balance at the beginning of the period	171	[2]	(26)	[2]	8		(27)	[2]
Total gains and losses (realized/unrealized):
Included in earnings			0	[2]			19	[2]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Gain (Loss) Included in Earnings	(9)	[2]			(3)
Included in OCI	0	[2]	0	[2]	0		0	[2]
Included in nuclear decommissioning obligations	0	[2]	0	[2]	0		0	[2]
Purchases	(109)	[2]	(2)	[2]	(1)		6	[2]
Transfer into Level 3			13	[1],[2]			(17)	[1]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3	(31)	[2]			4
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3	(20)	[2]			(6)
Transfer out of Level 3			8	[1],[2]			12	[1]
Balance at the end of the period	2	[2]	(7)	[2]	2	[2]	(7)	[2]
The amount of the total gains for the period included in earnings attributable to the change in unrealized gains relating to assets still held at the end of the period	$ (5)	[2]	$ (1)	[2]	$ 1		$ 6	[2]

[1] Transfers in/out of Level 3 are related to the availability of external broker quotes, and are valued as of the end of the reporting period. All transfers in/out are with Level 2.

[2] Consists of derivatives assets and liabilities, net.