Pension And OPEB (Components Of Net Periodic Benefit Cost) (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost	$ 37	$ 36	$ 113	$ 106
Interest Cost	35	48	105	144
Expected Return on Plan Assets	(119)	(111)	(357)	(332)
Amortization of Prior Service Cost	0	(3)	0	(8)
Amortization of Actuarial Loss	26	23	77	69
Non-Operating Pension and OPEB (Credits) Costs	(58)	(43)	(175)	(127)
Total Benefit (Credits) Costs	(21)	(7)	(62)	(21)
OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost	3	2	7	7
Interest Cost	5	8	16	25
Expected Return on Plan Assets	(10)	(10)	(31)	(29)
Amortization of Prior Service Cost	(33)	(32)	(97)	(96)
Amortization of Actuarial Loss	11	12	33	35
Non-Operating Pension and OPEB (Credits) Costs	(27)	(22)	(79)	(65)
Total Benefit (Credits) Costs	$ (24)	$ (20)	$ (72)	$ (58)