Employee Benefit Plans (Change in Fair Value of Company's Level 3 Pension Assets) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	$ 2,965
End balance	3,216	$ 2,965
Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	835	795
Realized gains/(losses)	30	53
Unrealized (losses)/gains	(7)	8
Transfers (out)/in, net	15	(22)
Foreign currency gains/(losses)	43	1
End balance	916	835
Level 3 | Real Estate
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	123	137
Realized gains/(losses)	4	18
Unrealized (losses)/gains	(5)	(7)
Transfers (out)/in, net	1	(27)
Foreign currency gains/(losses)	1	2
End balance	124	123
Level 3 | Other Debt Securities
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	377	359
Realized gains/(losses)	24	38
Unrealized (losses)/gains	0	0
Transfers (out)/in, net	(14)	(12)
Foreign currency gains/(losses)	34	(8)
End balance	421	377
Level 3 | Hedge Funds and Other Assets
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	335	299
Realized gains/(losses)	2	(3)
Unrealized (losses)/gains	(2)	15
Transfers (out)/in, net	28	17
Foreign currency gains/(losses)	8	7
End balance	$ 371	$ 335