Employee Benefits - Postretirement Benefits Other Than Pension Expenses (Detail) - Defined Contribution and Other Retirement Plans - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Defined Benefit Plan Disclosure [Line Items]
Interest cost on projected benefit obligation	$ 6	$ 0	$ 7	$ 1
Net amortization and deferrals	(16)	(1)	(18)	(3)
Net periodic benefit (income) cost	$ (10)	$ (1)	$ (11)	$ (2)