Retirement Benefits (Components Of Net Periodic Benefit Cost) (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total non-service cost components	$ (34)	$ (30)	$ (68)	$ (53)
Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service Cost	34	28	67	55
Interest cost	38	44	76	87
Expected return on plan assets	(74)	(72)	(149)	(145)
Prior service benefit	0	(1)	0	(1)
Actuarial loss (gain)	20	16	37	30
Total non-service cost components	(16)	(13)	(36)	(29)
Net periodic benefit cost (income)	18	15	31	26
Other Postretirement Benefit Plan, Defined Benefit
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service Cost	6	6	12	10
Interest cost	8	9	16	19
Expected return on plan assets	(20)	(20)	(40)	(40)
Prior service benefit	(1)	(1)	(2)	(2)
Actuarial loss (gain)	(2)	(2)	(3)	(4)
Total non-service cost components	(15)	(14)	(29)	(27)
Net periodic benefit cost (income)	$ (9)	$ (8)	$ (17)	$ (17)