Lease Cost (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Leases [Abstract]
Operating lease cost	$ 451	$ 481
Amortization of right-of-use assets	38	37
Interest on lease liabilities	21	24
Short-term lease cost	24	85
Total lease cost	$ 534	$ 627