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

[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.)