Fair Value Measurements (Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Millions		Sep. 30, 2016		Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments		$ 0		$ 64
Total assets		3,447		3,428
Electricity		136		170
Natural Gas		2		1
Total liabilities		138		171
Amount primarily related to deferred taxes on appreciation of investment value		346	[1]	314	[2]
Nuclear Decommissioning Trusts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments		1		36
Total assets		2,943	[1]	2,784	[2]
Fixed-income securities		1,250		1,215
Global equity securities		1,678		1,520
Financial Instruments Measured At NAV		14		13
Price Risk Management Instrument [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets		226		288
Electricity		216		286
Natural Gas		10		2
Rabbi Trusts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets		136		127
Fixed-income securities		59		57
Life insurance contracts		77		70
Long-Term Disability Trust [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments		4		7
Total assets		142		165
Financial Instruments Measured At NAV		138		158
Fair Value Measurements, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments		0		64
Total assets		2,413		2,321
Total liabilities		25		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		1		36
Total assets		2,399	[1]	2,250	[2]
Fixed-income securities		720		694
Global equity securities		1,678		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		10		0
Electricity		10		0
Natural Gas		0		0
Electricity		25		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		4		7
Total assets		4		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		692		658
Total liabilities		10		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		530	[1]	521	[2]
Fixed-income securities		530		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		26		10
Electricity		16		9
Natural Gas		10		1
Electricity		8		1
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		136		127
Fixed-income securities		59		57
Life insurance contracts		77		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		192		259
Total liabilities		136		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		192		259
Electricity		192		259
Natural Gas		0		0
Electricity		136		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]	(33)		(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]	(2)		18
Natural Gas	[3]	0		1
Electricity	[3]	(33)		(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 $346 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.