Employee Benefit Plans (Components of Net Periodic Benefit Cost (Credit) (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 3	$ 3	$ 7	$ 10
Interest cost	5	6	15	18
Expected return on assets	(12)	(11)	(36)	(33)
Amortization of actuarial losses	1	2	4	5
Net periodic benefit cost (credit)	(3)	0	(10)	0
Expected return on assets	12	11	36	33
Amortization of actuarial losses	(1)	(2)	(4)	(5)
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	1	1	3
Interest cost	1	2	4	6
Expected return on assets	0	0	0	0
Amortization of actuarial losses	0	0	0	0
Net periodic benefit cost (credit)	1	3	5	9
Expected return on assets	0	0	0	0
Amortization of actuarial losses	$ 0	$ 0	$ 0	$ 0