Employee Benefit Plans (Change in Fair Value of Company's Level 3 Pension Assets) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	$ 2,561
End balance	2,883	$ 2,561
Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	515	635
Realized gains	59	29
Unrealized losses	5	(16)
Transfers (out)/in	386	(77)
Foreign currency losses	37	(56)
End balance	1,002	515
Level 3 | Real Estate
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	129	209
Realized gains	11	28
Unrealized losses	0	(15)
Transfers (out)/in	(5)	(88)
Foreign currency losses	3	(5)
End balance	138	129
Level 3 | Other Debt Securities
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	16	21
Realized gains	45	1
Unrealized losses	0	0
Transfers (out)/in	355	(5)
Foreign currency losses	2	(1)
End balance	418	16
Level 3 | Hedge Funds and Other Assets
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	370	405
Realized gains	3	0
Unrealized losses	5	(1)
Transfers (out)/in	36	16
Foreign currency losses	32	(50)
End balance	$ 446	$ 370