Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2011

Fair Value Measurements [Abstract]

Assets and liabilities measured at fair value on a recurring basis

	Fair Value Measurements Using
As of December 31, 2011:	Quoted Prices     in Active     Markets for     Identical     Assets     (Level 1)	Significant Other Observable Inputs (Level 2)	Significant Unobservable Inputs (Level 3)	Total
	(in millions)
Assets:
Energy-related derivatives	$    —	$  14	$—	$	14
Interest rate derivatives	—	13	—		13
Foreign currency derivatives	—	2	—		2
Nuclear decommissioning trusts: (a)
Domestic equity	396	58	—		454
Foreign equity	124	48	—		172
U.S. Treasury and government agency securities	17	33	—		50
Municipal bonds	—	82	—		82
Corporate bonds	—	260	—		260
Mortgage and asset backed securities	—	151	—		151
Other investments	—	36	—		36
Cash equivalents and restricted cash	1,024	—	—		1,024
Other investments	3	50	14		67
Total	$1,564	$747	$14	$	2,325
Liabilities:
Energy-related derivatives	$    —	$245	$—	$	245
Interest rate derivatives	—	33	—		33
Foreign currency derivatives	—	3	—		3
Total	$    —	$281	$—	$	281

(a) Includes the investment securities pledged to creditors and collateral received, and excludes receivables related to investment income, pending investment sales, and payables related to pending investment purchases and the lending pool. See Note 1 under “Nuclear Decommissioning” for additional information.

As of December 31, 2010, assets and liabilities measured at fair value on a recurring basis during the period, together with the level of the fair value hierarchy in which they fall, were as follows:

	Fair Value Measurements Using
As of December 31, 2010:	Quoted Prices in Active Markets for Identical Assets (Level 1)	Significant Other Observable Inputs (Level 2)	Significant Unobservable Inputs (Level 3)	Total
	(in millions)
Assets:
Energy-related derivatives	$ —	$  10	$—	$	10
Interest rate derivatives	—	10	—		10
Foreign currency derivatives	—	3	—		3
Nuclear decommissioning trusts: (a)
Domestic equity	604	60	—		664
U.S. Treasury and government agency securities	20	220	—		240
Municipal bonds	—	53	—		53
Corporate bonds	—	220	—		220
Mortgage and asset backed securities	—	119	—		119
Other investments	—	74	—		74
Cash equivalents and restricted cash	351	—	—		351
Other investments	9	51	19		79
Total	$984	$820	$ 19	$	1,823
Liabilities:
Energy-related derivatives	$ —	$206	$—	$	206
Interest rate derivatives	—	1	—		1
Total	$ —	$207	$—	$	207

(a) Includes the investment securities pledged to creditors and collateral received, and excludes receivables related to investment income, pending investment sales, and payables related to pending investment purchases and the lending pool. See Note 1 under “Nuclear Decommissioning” for additional information.

Fair value measurements of investments calculated at net asset value per share as well as the nature and risk of those investments

	Fair Value	Unfunded Commitments	Redemption Frequency	Redemption  Notice Period
As of December 31, 2011:	(in millions)
Nuclear decommissioning trusts:
Corporate bonds – commingled funds	$    32	None	Daily	1 to 3 days
Equity – commingled funds	48	None	Daily/Monthly	Daily/7 days
Other – commingled funds	25	None	Daily	Not applicable
Trust-owned life insurance	87	None	Daily	15 days
Cash equivalents and restricted cash:
Money market funds	1,024	None	Daily	Not applicable
As of December 31, 2010:
Nuclear decommissioning trusts:
Corporate bonds – commingled funds	$    65	None	Daily	1 to 3 days
Other – commingled funds	67	None	Daily	Not applicable
Trust-owned life insurance	86	None	Daily	15 days
Cash equivalents and restricted cash:
Money market funds	351	None	Daily	Not applicable
Other:
Money market funds	2	None	Daily	Not applicable

Financial instruments not having carrying amount equal to fair value

	Carrying Amount	Fair Value
	(in millions)
Long-term debt:
2011	$20,272	$22,144
2010	$19,356	$20,073