Employee Postretirement Benefits - Schedule of Amounts Recognized in Balance Sheet (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Accrued benefit costs and other current liabilities	$ (1)	$ (5)
Deferred credits and other liabilities	(42)	(68)
Net amount recognized at end of year	(43)	(73)
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Accrued benefit costs and other current liabilities	(11)	(10)
Deferred credits and other liabilities	(156)	(137)
Net amount recognized at end of year	$ (167)	$ (147)