Retirement Benefits (Components Of Net Periodic Benefit Cost) (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total non-service cost components	$ (32)	$ (23)	$ (85)	$ (67)
Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	28	22	83	66
Interest cost	43	46	130	139
Expected return on plan assets	(73)	(69)	(218)	(207)
Prior service cost (benefit)	0	0	(1)	0
Actuarial loss (gain)	15	6	45	19
Total non-service cost components	(15)	(17)	(44)	(49)
Net periodic benefit cost (income)	13	5	39	17
Other Postretirement Benefit Plan, Defined Benefit
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	4	4	14	13
Interest cost	10	11	29	32
Expected return on plan assets	(20)	(19)	(60)	(57)
Prior service cost (benefit)	(1)	(1)	(3)	(4)
Actuarial loss (gain)	(3)	(4)	(7)	(11)
Total non-service cost components	(14)	(13)	(41)	(40)
Net periodic benefit cost (income)	$ (10)	$ (9)	$ (27)	$ (27)