Pension and Other Postretirement Benefits - Schedule of Amounts Expected to be Recognized in Net Periodic Benefit Cost (Detail) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Pension benefits
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss recognition	$ 139
Prior service cost (benefit) recognition	$ 2
Other postretirement benefits
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss recognition		$ 3
Prior service cost (benefit) recognition		$ (4)