Fair Value Measurements (Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amount primarily related to deferred taxes on appreciation of investment value	$ 324		$ 313
Estimate Of Fair Value Fair Value Disclosure [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market investments	94		226
Total assets	3,399		3,374
Other investments	33		84
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market investments	94		226
Total assets	2,478		2,622
Other investments	33		84
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	687		643
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	232		107
Netting [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	2	[1]	2	[1]
Nuclear Decommissioning Trusts [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market investments	17		38
U.S. equity securities			1,046
Non-U.S. equity securities			457
Global equity securities	1,585
Fixed-income securities	741
U.S. government and agency securities			760
Municipal securities			0
Other fixed-income securities			0
Total assets	2,343	[2]	2,301	[3]
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			11
Non-U.S. equity securities			0
Global equity securities	13
Fixed-income securities	389
U.S. government and agency securities			156
Municipal securities			25
Other fixed-income securities			162
Total assets	402	[2]	354	[3]
Nuclear Decommissioning Trusts [Member] | Estimate Of Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market investments	17		38
U.S. equity securities			1,057
Non-U.S. equity securities			457
Global equity securities	1,598
Fixed-income securities	1,130
U.S. government and agency securities			916
Municipal securities			25
Other fixed-income securities			162
Total assets	2,745	[2]	2,655	[3]
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	1		2
Electric	0		2
Gas	1		0
Electric	47		19
Gas	0		1
Total liabilities	47		20
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	18		32
Electric	17		27
Gas	1		5
Electric	5		72
Gas	3		3
Total liabilities	8		75
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	232		107
Electric	232		107
Electric	163		137
Total liabilities	163		137
Price Risk Management Instruments [Member] | Netting [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	2	[1]	2	[1]
Electric	2	[1]	3	[1]
Gas	0	[1]	(1)	[1]
Electric	(52)	[1]	(84)	[1]
Gas	0	[1]	(1)	[1]
Total liabilities	(52)	[1]	(85)	[1]
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	253		143
Electric	251		139
Gas	2		4
Electric	163		144
Gas	3		3
Total liabilities	166		147
Rabbi Trusts [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed-income securities	42		39
Life insurance contracts	72		70
Total assets	114		109
Rabbi Trusts [Member] | Estimate Of Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed-income securities	42		39
Life insurance contracts	72		70
Total assets	114		109
Long-Term Disability Trust [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market investments	7		9
Total assets	7		9
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			14
Non-U.S. equity securities			12
Global equity securities	25
Fixed-income securities	128		122
Total assets	153		148
Long-Term Disability Trust [Member] | Estimate Of Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market investments	7		9
U.S. equity securities			14
Non-U.S. equity securities			12
Global equity securities	25
Fixed-income securities	128		122
Total assets	$ 160		$ 157

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

[2] Represents amount before deducting $324 million, primarily related to deferred taxes on appreciation of investment value.

[3] Represents amount before deducting $313 million, primarily related to deferred taxes on appreciation of investment value.