Employee Benefit Plans (Net Periodic Benefit Costs) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 8	$ 10	$ 10
Interest cost	26	24	24
Amortization of prior service credit	(57)	(60)	(59)
Amortization of actuarial losses	8	19	12
Net periodic benefit cost/(income)	(15)	(7)	(13)
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	23	28	33
Interest cost	105	97	98
Expected return on plan assets	139	150	141
Amortization of prior service credit	0
Amortization of actuarial losses	62	63	75
Settlements, curtailments, and special termination benefits	3	5	60
Net periodic benefit cost/(income)	$ 54	$ 43	$ 125