New And Significant Accounting Policies (Reclassifications Out Of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2017		Sep. 30, 2016		Sep. 30, 2017	Sep. 30, 2016
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance	$ (8)		$ (7)		$ (9)	$ (7)
Net current period other comprehensive income (loss)	0		0		1	0
Ending balance	(8)		(7)		(8)	(7)
Net actuarial loss tax	0		0		0	0
Amounts Reclassified From Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Amortization of prior service cost	1	[1]	3	[1]	4	10
Amortization of net actuarial loss	5	[1]	4	[1]	12	13
Regulatory account transfer	(6)	[1]	(7)	[1]	(15)	(23)
Pension Benefits [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance	(25)		(23)		(25)	(23)
Amortization of prior service cost	(1)		2		(5)	6
Amortization of net actuarial loss	6		6		17	18
Net current period other comprehensive income (loss)	0		0		0	0
Ending balance	(25)		(23)		(25)	(23)
Pension Benefits [Member] | Amounts Reclassified From Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Amortization of prior service cost	(1)	[1]	2	[1]	(3)	4
Amortization of net actuarial loss	4	[1]	3	[1]	10	11
Regulatory account transfer	(3)	[1]	(5)	[1]	(7)	(15)
Amortization of prior service cost tax	0		0		2	2
Net actuarial loss tax	2		3		7	7
Regulatory account transfer tax	2		3		5	9
Other Benefits [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance	17		16		16	16
Amortization of prior service cost	4		3		12	11
Amortization of net actuarial loss	1		1		3	3
Net current period other comprehensive income (loss)	0		0		1	0
Ending balance	17		16		17	16
Other Benefits [Member] | Amounts Reclassified From Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Amortization of prior service cost	2	[1]	1	[1]	7	6
Amortization of net actuarial loss	1	[1]	1	[1]	2	2
Regulatory account transfer	(3)	[1]	(2)	[1]	(8)	(8)
Amortization of prior service cost tax	2		2		5	5
Net actuarial loss tax	0		0		1	1
Regulatory account transfer tax	$ 2		$ 2		$ 6	$ 6

[1] These components are included in the computation of net periodic pension and other postretirement benefit costs. (See the Pension and Other Postretirement Benefits table above for additional details.)