New And Significant Accounting Policies (Reclassifications Out Of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance		$ (7)	$ (6)	$ (7)	$ 11
Change in investments		0	0	0	(17)
Net current period other comprehensive income (loss)		0	0	0	(17)
Ending balance		(7)	(6)	(7)	(6)
Net change in investments tax		0	0	0	12
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]	3	5	10	15
Amortization of net actuarial loss	[1]	4	2	13	6
Regulatory account transfer	[1]	(7)	(7)	(23)	(21)
Change in investments					(17)
Pension Benefits [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance		(23)	(21)	(23)	(21)
Amortization of prior service cost		2	4	6	11
Amortization of net actuarial loss		6	1	18	7
Net current period other comprehensive income (loss)		0	0	0	0
Ending balance		(23)	(21)	(23)	(21)
Pension Benefits [Member] | Amounts Reclassified From Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Amortization of prior service cost	[1]	2	3	4	7
Amortization of net actuarial loss	[1]	3	1	11	4
Regulatory account transfer	[1]	(5)	(4)	(15)	(11)
Change in investments					0
Amortization of prior service cost tax		0	1	2	4
Net actuarial loss tax		3	0	7	3
Regulatory account transfer tax		3	3	9	7
Change in investments tax				0	0
Other Benefits [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance		16	15	16	15
Amortization of prior service cost		3	4	11	14
Amortization of net actuarial loss		1	1	3	3
Net current period other comprehensive income (loss)		0	0	0	0
Ending balance		16	15	16	15
Other Benefits [Member] | Amounts Reclassified From Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Amortization of prior service cost	[1]	1	2	6	8
Amortization of net actuarial loss	[1]	1	1	2	2
Regulatory account transfer	[1]	(2)	(3)	(8)	(10)
Change in investments					0
Amortization of prior service cost tax		2	2	5	6
Net actuarial loss tax		0	0	1	1
Regulatory account transfer tax		$ 2	3	6	7
Change in investments tax				0	0
Other Investments [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance					17
Net current period other comprehensive income (loss)					(17)
Ending balance			$ 0		0
Other Investments [Member] | Amounts Reclassified From Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Amortization of prior service cost	[1]				0
Amortization of net actuarial loss	[1]				0
Regulatory account transfer	[1]				0
Change in investments					(17)
Change in investments tax				$ 0	$ 12

[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.)