Leases - Summary of Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	$ 48	$ 98
Operating cash flows from finance leases	0	0
Financing cash flows from finance leases	2	2
Right-of-use assets obtained in exchange for new lease obligations:
Operating leases	21	39
Finance leases	$ 30	$ 30