Employee Benefit Plans (Net Periodic Benefit Costs) (Detail) - Pensions - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 33	$ 48
Interest cost	98	142
Amortization of prior service (cost) credit	(1)
Amortization of actuarial losses	(68)
Settlements, curtailments, and special termination benefits	85	2,354
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 (cost) credit		(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
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	10	15	16
Interest cost	24	31	45
Amortization of prior service (cost) credit	(59)	(31)	(9)
Amortization of actuarial losses	12	19	32
Net periodic benefit cost/(income)	$ (13)	$ 34	$ 84