Leases - Schedule of Consolidated Balance Sheet Information Related to Operating and Finance Leases (Detail) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Leases [Abstract]
Operating lease right-of-use assets — net	$ 713	$ 0
Operating Leases, Lease obligations:
Operating Leases, Lease Liabilities, Current	366
Long-term operating lease obligations	436	0
Operating Leases, Total lease obligations	802
Finance lease right-of-use assets — net	332	0
Financing Leases, Lease obligations:
Financing Leases, Lease liabilities, Current	36
Financing Leases, Lease liabilities, Long-term	250	$ 0
Financing Leases, Total lease obligations	$ 286