Leases - Summary of Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2019	Sep. 30, 2018
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	$ 53	$ 151
Operating cash flows from finance leases	1	1	$ 0
Financing cash flows from finance leases	2	4
Right-of-use assets obtained in exchange for new lease obligations:
Operating leases	18	57
Finance leases	$ 0	$ 30