Retirement Benefits (Components Of Net Periodic Benefit Cost) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total non-service cost components	$ (34)	$ (23)
Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	33	27
Interest cost	38	43
Expected return on plan assets	(75)	(73)
Prior service cost (benefit)	0	0
Actuarial loss (gain)	17	14
Total non-service cost components	(20)	(16)
Net periodic benefit cost (income)	13	11
Other Postretirement Benefit Plan, Defined Benefit
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	6	4
Interest cost	8	10
Expected return on plan assets	(20)	(20)
Prior service cost (benefit)	(1)	(1)
Actuarial loss (gain)	(1)	(2)
Total non-service cost components	(14)	(13)
Net periodic benefit cost (income)	$ (8)	$ (9)