Employee Benefit Plans (Net Periodic Benefit Costs) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 10	$ 10	$ 15
Interest cost	24	24	31
Amortization of prior service credit	(60)	(59)	(31)
Amortization of actuarial losses	19	12	19
Net periodic benefit cost/(income)	(7)	(13)	34
United States
Defined Benefit Plan Disclosure [Line Items]
Service cost	28	33	48
Interest cost	97	98	142
Expected return on plan assets	150	141	213
Amortization of prior service credit	0		(1)
Amortization of actuarial losses	63	75	110
Settlements, curtailments, and special termination benefits	5	60	1,015
Net periodic benefit cost/(income)	$ 43	$ 125	$ 1,101