Leases - Maturities (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Jan. 01, 2019
Operating Leases
2021	$ 469
2022	411
2023	331
2024	232
2025	177
Thereafter	592
Total lease payments	2,212
Less: interest	(428)
Total	1,784		$ 2,200
Less: current portion	(379)	$ (416)
Long-term portion	1,405	1,342
Finance Leases
2021	40
2022	32
2023	29
2024	28
2025	29
Thereafter	240
Total lease payments	398
Less: interest	(105)
Total	293
Less: current portion	(26)	(35)
Long-term portion	$ 267	$ 185