Fair Value Measurements (Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Millions	Sep. 30, 2017		Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	$ 120		$ 105
Total assets	3,755		3,575
Electricity	105		126
Natural Gas	2		1
Total liabilities	107		127
Amount primarily related to deferred taxes on appreciation of investment value	387	[1]	333	[2]
Nuclear Decommissioning Trusts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	23		9
Total assets	3,180	[1]	2,939	[2]
Fixed-income securities	1,266		1,192
Global equity securities	1,875		1,724
Financial Instruments Measured At NAV	16		14
Price Risk Management Instrument [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	167		222
Electricity	163		211
Natural Gas	4		11
Rabbi Trusts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	135		131
Fixed-income securities	64		61
Life insurance contracts	71		70
Long-Term Disability Trust [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	5		8
Total assets	153		178
Financial Instruments Measured At NAV	148		170
Fair Value Measurements, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	120		105
Total assets	2,724		2,541
Total liabilities	11		9
Fair Value Measurements, Level 1 [Member] | Nuclear Decommissioning Trusts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	23		9
Total assets	2,595	[1]	2,398	[2]
Fixed-income securities	697		665
Global equity securities	1,875		1,724
Financial Instruments Measured At NAV	0		0
Fair Value Measurements, Level 1 [Member] | Price Risk Management Instrument [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	4		30
Electricity	4		30
Natural Gas	0		0
Electricity	11		9
Natural Gas	0		0
Fair Value Measurements, Level 1 [Member] | Rabbi Trusts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	0		0
Fixed-income securities	0		0
Life insurance contracts	0		0
Fair Value Measurements, Level 1 [Member] | Long-Term Disability Trust [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	5		8
Total assets	5		8
Financial Instruments Measured At NAV	0		0
Fair Value Measurements, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	0		0
Total assets	715		687
Total liabilities	19		14
Fair Value Measurements, Level 2 [Member] | Nuclear Decommissioning Trusts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	0		0
Total assets	569	[1]	527	[2]
Fixed-income securities	569		527
Global equity securities	0		0
Financial Instruments Measured At NAV	0		0
Fair Value Measurements, Level 2 [Member] | Price Risk Management Instrument [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	11		29
Electricity	7		18
Natural Gas	4		11
Electricity	17		12
Natural Gas	2		2
Fair Value Measurements, Level 2 [Member] | Rabbi Trusts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	135		131
Fixed-income securities	64		61
Life insurance contracts	71		70
Fair Value Measurements, Level 2 [Member] | Long-Term Disability Trust [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	0		0
Total assets	0		0
Financial Instruments Measured At NAV	0		0
Fair Value Measurements, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	0		0
Total assets	153		181
Total liabilities	105		126
Fair Value Measurements, Level 3 [Member] | Nuclear Decommissioning Trusts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	0		0
Total assets	0	[1]	0	[2]
Fixed-income securities	0		0
Global equity securities	0		0
Financial Instruments Measured At NAV	0		0
Fair Value Measurements, Level 3 [Member] | Price Risk Management Instrument [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	153		181
Electricity	153		181
Natural Gas	0		0
Electricity	105		126
Natural Gas	0		0
Fair Value Measurements, Level 3 [Member] | Rabbi Trusts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	0		0
Fixed-income securities	0		0
Life insurance contracts	0		0
Fair Value Measurements, Level 3 [Member] | Long-Term Disability Trust [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	0		0
Total assets	0		0
Financial Instruments Measured At NAV	0		0
Netting [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	0		0	[3]
Total assets	(1)		(18)	[3]
Total liabilities	(28)		(22)	[3]
Netting [Member] | Nuclear Decommissioning Trusts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	0		0	[3]
Total assets	0	[1]	0	[2],[3]
Fixed-income securities	0		0	[3]
Global equity securities	0		0	[3]
Financial Instruments Measured At NAV	0		0	[3]
Netting [Member] | Price Risk Management Instrument [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	(1)		(18)	[3]
Electricity	(1)		(18)	[3]
Natural Gas	0		0	[3]
Electricity	(28)		(21)	[3]
Natural Gas	0		(1)	[3]
Netting [Member] | Rabbi Trusts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	0		0	[3]
Fixed-income securities	0		0	[3]
Life insurance contracts	0		0	[3]
Netting [Member] | Long-Term Disability Trust [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	0		0	[3]
Total assets	0		0	[3]
Financial Instruments Measured At NAV	$ 0		$ 0	[3]

[1] Represents amount before deducting $387 million, primarily related to deferred taxes on appreciation of investment value.

[2] Represents amount before deducting $333 million, primarily related to deferred taxes on appreciation of investment value.

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