Leases - Supplemental Cash Flow Information Related to Leases (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Cash paid for amounts included in the measurement of lease obligations:
Operating Leases, Operating cash flows	$ 106
Operating Leases, Financing cash flows	0
Finance Leases, Operating cash flows	6
Finance Leases, Financing cash flows	23	$ 0
Noncash transactions:
Operating Leases, Leased assets recognized for new lease obligations incurred	3
Finance Leases, Leased assets recognized for new lease obligations incurred	$ 0