Employee Benefit Plans (Components of Net Periodic Benefit Cost (Credit) (Detail) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost		$ 3	$ 4	$ 10	$ 11
Interest cost		6	6	18	21
Expected return on assets		(11)	(11)	(33)	(31)
Amortization of actuarial losses		2	2	5	9
Curtailment	[1]			0	6
Settlement loss	[1]	0	11	0	11
Net periodic benefit cost		0	12	0	27
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost		1	1	3	2
Interest cost		2	2	6	6
Expected return on assets		0	0	0	0
Amortization of actuarial losses		0	0	0	0
Curtailment	[1]			0	3
Settlement loss	[1]	0	0	0	0
Net periodic benefit cost		$ 3	$ 3	$ 9	$ 11

[1] Related to a voluntary retirement program.