Leases - Other Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Leases [Abstract]
Operating cash flows for operating leases	$ 1,053	$ 1,166	$ 1,271
Operating cash flows for finance leases	32	27	22
Financing cash flows for finance leases	$ 255	$ 192	$ 108