New And Significant Accounting Policies (Reclassifications Out Of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2017	Mar. 31, 2016
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance		$ (9)	$ (7)
Net current period other comprehensive income (loss)		0	0
Ending balance		(9)	(7)
Net actuarial loss tax		0	0
Amounts Reclassified From Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Amortization of prior service cost	[1]	1	3
Amortization of net actuarial loss	[1]	4	5
Regulatory account transfer	[1]	(5)	(8)
Pension Benefits [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance		(25)	(23)
Amortization of prior service cost		(2)	2
Amortization of net actuarial loss		6	6
Net current period other comprehensive income (loss)		0	0
Ending balance		(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)	1
Amortization of net actuarial loss	[1]	3	4
Regulatory account transfer	[1]	(2)	(5)
Amortization of prior service cost tax		1	1
Net actuarial loss tax		3	2
Regulatory account transfer tax		2	3
Other Benefits [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance		16	16
Amortization of prior service cost		4	4
Amortization of net actuarial loss		1	1
Net current period other comprehensive income (loss)		0	0
Ending balance		16	16
Other Benefits [Member] | Amounts Reclassified From Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Amortization of prior service cost	[1]	2	2
Amortization of net actuarial loss	[1]	1	1
Regulatory account transfer	[1]	(3)	(3)
Amortization of prior service cost tax		2	2
Net actuarial loss tax		0	0
Regulatory account transfer tax		$ 2	$ 2

[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.)