Pension, OPEB and Savings Plans (Pre-Tax Changes Recognized In Accumulated Other Comprehensive Income (Loss), Regulatory Assets And Deferred Assets) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net Actuarial (Gain) Loss in Current Period	$ 55	$ 211
Amortization of Net Actuarial Gain (Loss)	(97)	(158)
Prior Service Cost (Credit) in current period	0	1
Amortization of Prior Service Credit	18	19
Total	(24)	73
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net Actuarial (Gain) Loss in Current Period	156	125
Amortization of Net Actuarial Gain (Loss)	(50)	(40)
Prior Service Cost (Credit) in current period	0	(3)
Amortization of Prior Service Credit	11	14
Total	$ 117	$ 96