Employee Benefit Plans (Net Periodic Benefit Costs) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 10	$ 15	$ 16
Interest cost	24	31	45
Amortization of prior service credit	(59)	(31)	(9)
Amortization of actuarial losses	12	19	32
Net periodic benefit cost/(income)	(13)	34	84
Pensions
Defined Benefit Plan Disclosure [Line Items]
Service cost	33	48	57
Interest cost	98	142	196
Expected return on plan assets	141	213	287
Amortization of prior service credit	1	(1)	(2)
Amortization of actuarial losses	75	110	119
Settlements, curtailments, and special termination benefits	60	1,015	8
Net periodic benefit cost/(income)	$ 125	$ 1,101	$ 91