Employee Benefit Plans (Components of Net Periodic Benefit Cost) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 12	$ 15	$ 17
Interest cost	24	28	29
Expected return on assets	(45)	(40)	(48)
Prior service cost amortization	0	0	0
Amortization of actuarial losses	6	11	11
Settlement loss	7	16	0
Curtailment	0	6	0
Net periodic benefit cost	4	36	9
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	3	3	4
Interest cost	8	9	8
Amortization of actuarial losses		0	0
Settlement loss	0
Curtailment	0	3	0
Net periodic benefit cost	$ 11	$ 15	$ 12