Fair Value Measurements (Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Millions		Mar. 31, 2016		Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments		$ 97		$ 64
Total assets		3,495		3,428
Electricity		171		170
Natural Gas		1		1
Total liabilities		172		171
Amount primarily related to deferred taxes on appreciation of investment value		331		314
Nuclear Decommissioning Trusts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments		25		36
Total assets		2,847	[1]	2,784	[2]
Fixed-income securities		1,190		1,215
Global equity securities		1,619		1,520
Financial Instruments Measured At NAV		13		13
Price Risk Management Instrument [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets		266		288
Electricity		262		286
Natural Gas		4		2
Rabbi Trusts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets		130		127
Fixed-income securities		58		57
Life insurance contracts		72		70
Long-Term Disability Trust [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments		8		7
Total assets		155		165
Financial Instruments Measured At NAV		147		158
Fair Value Measurements, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments		97		64
Total assets		2,434		2,321
Total liabilities		67		69
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		25		36
Total assets		2,326	[1]	2,250	[2]
Fixed-income securities		682		694
Global equity securities		1,619		1,520
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		3		0
Electricity		1		0
Natural Gas		2		0
Electricity		67		69
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		8		7
Total assets		8		7
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		653		658
Total liabilities		6		3
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		508	[1]	521	[2]
Fixed-income securities		508		521
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		15		10
Electricity		12		9
Natural Gas		3		1
Electricity		5		1
Natural Gas		1		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		130		127
Fixed-income securities		58		57
Life insurance contracts		72		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		246		259
Total liabilities		171		170
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		246		259
Electricity		246		259
Natural Gas		0		0
Electricity		171		170
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	[3]	0		0
Total assets	[3]	2		19
Total liabilities	[3]	(72)		(71)
Netting [Member] | Nuclear Decommissioning Trusts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	[3]	0		0
Total assets	[3]	0	[1]	0	[2]
Fixed-income securities	[3]	0		0
Global equity securities	[3]	0		0
Financial Instruments Measured At NAV	[3]	0		0
Netting [Member] | Price Risk Management Instrument [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	[3]	2		19
Electricity	[3]	3		18
Natural Gas	[3]	(1)		1
Electricity	[3]	(72)		(70)
Natural Gas	[3]	0		(1)
Netting [Member] | Rabbi Trusts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	[3]	0		0
Fixed-income securities	[3]	0		0
Life insurance contracts	[3]	0		0
Netting [Member] | Long-Term Disability Trust [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	[3]	0		0
Total assets	[3]	0		0
Financial Instruments Measured At NAV	[3]	$ 0		$ 0

[1] Represents amount before deducting $331 million, primarily related to deferred taxes on appreciation of investment value.

[2] Represents amount before deducting $314 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.