Leases - Summary of Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	$ 171	$ 175
Operating cash flows from finance leases	1	1	$ 0
Financing cash flows from finance leases	11	6
Right-of-use assets obtained in exchange for new lease obligations:
Operating leases	88	93
Finance leases	$ 0	$ 34