Retirement Benefits (Components Of Net Periodic Benefit Cost) (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total non-service cost components	$ (30)	$ (22)	$ (53)	$ (44)
Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	28	22	55	44
Interest cost	44	46	87	93
Expected return on plan assets	(72)	(69)	(145)	(138)
Prior service cost (benefit)	(1)	0	(1)	0
Actuarial loss (gain)	16	7	30	13
Total non-service cost components	(13)	(16)	(29)	(32)
Net periodic benefit cost (income)	15	6	26	12
Other Postretirement Benefit Plan, Defined Benefit
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	6	5	10	9
Interest cost	9	10	19	21
Expected return on plan assets	(20)	(19)	(40)	(38)
Prior service cost (benefit)	(1)	(2)	(2)	(3)
Actuarial loss (gain)	(2)	(3)	(4)	(7)
Total non-service cost components	(14)	(14)	(27)	(27)
Net periodic benefit cost (income)	$ (8)	$ (9)	$ (17)	$ (18)