Fair Value Measurements (Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) (USD $) In Millions	Sep. 30, 2011		Dec. 31, 2010
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Correction in the classification of Level 3 price risk management instruments			$ 125
Amount primarily related to deferred taxes on appreciation of investment value	169		185
Nuclear Decommissioning Trusts [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
U.S. equity securities	786		1,029
Non-U.S. equity securities	311		349
U.S. government and agency securities	715		584
Municipal securities
Other fixed-income securities
Total assets	1,812	[1]	1,962	[1]
Nuclear Decommissioning Trusts [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
U.S. equity securities	12		7
Non-U.S. equity securities
U.S. government and agency securities	150		40
Municipal securities	65		119
Other fixed-income securities	94		66
Total assets	321	[1]	232	[1]
Nuclear Decommissioning Trusts [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
U.S. equity securities
Non-U.S. equity securities
U.S. government and agency securities
Municipal securities
Other fixed-income securities
Total assets		[1]		[1]
Nuclear Decommissioning Trusts [Member] | Netting [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
U.S. equity securities		[2]		[2]
Non-U.S. equity securities		[2]		[2]
U.S. government and agency securities		[2]		[2]
Municipal securities		[2]		[2]
Other fixed-income securities		[2]		[2]
Total assets		[1],[2]		[1],[2]
Nuclear Decommissioning Trusts [Member] | Estimate Of Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
U.S. equity securities	798		1,036
Non-U.S. equity securities	311		349
U.S. government and agency securities	865		624
Municipal securities	65		119
Other fixed-income securities	94		66
Total assets	2,133	[1]	2,194	[1]
Price Risk Management Instruments [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets			6
Electric			6
Gas
Electric	299		235
Gas	49		41
Price Risk Management Instruments [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets			2
Electric			2
Gas
Electric	12		73
Gas	3		1
Price Risk Management Instruments [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	175		125
Electric	166		119
Gas	9		6
Electric	448		475
Gas	8		49
Price Risk Management Instruments [Member] | Netting [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	23	[2]	68	[2]
Electric	24	[2]	63	[2]
Gas	(1)	[2]	5	[2]
Electric	(329)	[2]	(315)	[2]
Gas	(52)	[2]	(41)	[2]
Price Risk Management Instruments [Member] | Estimate Of Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	198		201
Electric	190		190
Gas	8		11
Electric	430		468
Gas	8		50
Rabbi Trusts [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other fixed-income securities
Life insurance contracts
Total assets
Rabbi Trusts [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other fixed-income securities	26		24
Life insurance contracts	67		65
Total assets	93		89
Rabbi Trusts [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other fixed-income securities
Life insurance contracts
Total assets
Rabbi Trusts [Member] | Netting [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other fixed-income securities		[2]		[2]
Life insurance contracts		[2]		[2]
Total assets		[2]		[2]
Rabbi Trusts [Member] | Estimate Of Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other fixed-income securities	26		24
Life insurance contracts	67		65
Total assets	93		89
Long-Term Disability Trust [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
U.S. equity securities	4		11
Non-U.S. equity securities
Fixed-income securities
Total assets	4		11
Long-Term Disability Trust [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
U.S. equity securities	13		24
Non-U.S. equity securities	9
Fixed-income securities	132		150
Total assets	154		174
Long-Term Disability Trust [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
U.S. equity securities
Non-U.S. equity securities
Fixed-income securities
Total assets
Long-Term Disability Trust [Member] | Netting [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
U.S. equity securities		[2]		[2]
Non-U.S. equity securities		[2]		[2]
Fixed-income securities		[2]		[2]
Total assets		[2]		[2]
Long-Term Disability Trust [Member] | Estimate Of Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
U.S. equity securities	17		35
Non-U.S. equity securities	9
Fixed-income securities	132		150
Total assets	158		185
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market investments	223		138
Total assets	2,039		2,117
Total liabilities	348		276
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market investments
Total assets	568		497
Total liabilities	15		74
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market investments
Total assets	175		125
Total liabilities	456		524
Netting [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market investments		[2]		[2]
Total assets	23	[2]	68	[2]
Total liabilities	(381)	[2]	(356)	[2]
Estimate Of Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market investments	223		138
Total assets	2,805		2,807
Total liabilities	$ 438		$ 518

[1] Excludes $169 million and $185 million at September 30, 2011 and December 31, 2010, respectively, primarily related to deferred taxes on appreciation of investment value.

[2] Includes the effect of the contractual ability to settle contracts under master netting agreements and margin cash collateral.