Pension And OPEB (Components Of Net Periodic Benefit Cost) (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost	$ 28	$ 33	$ 57	$ 65
Interest Cost	58	52	116	104
Expected Return on Plan Assets	(96)	(110)	(193)	(220)
Amortization of Prior Service Cost	(4)	(5)	(9)	(9)
Amortization of Actuarial Loss	27	21	54	42
Non-Operating Pension and OPEB (Credits) Costs	(15)	(42)	(32)	(83)
Total Benefit Costs	13	(9)	25	(18)
OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost	3	5	5	9
Interest Cost	11	17	22	33
Expected Return on Plan Assets	(9)	(11)	(18)	(21)
Amortization of Prior Service Cost	(32)	0	(64)	0
Amortization of Actuarial Loss	12	16	25	32
Non-Operating Pension and OPEB (Credits) Costs	(18)	22	(35)	44
Total Benefit Costs	$ (15)	$ 27	$ (30)	$ 53