Leases - Future Maturities of Lease Liabilities - ASC 842 (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Operating Leases
2021	$ 245
2022	186
2023	146
2024	110
2025	88
Thereafter	376
Total Lease Payments	1,151
Less: Imputed Interest	269
Total Operating Lease Liabilities	882	$ 867
Finance Leases
2021	38
2022	23
2023	21
2024	21
2025	22
Thereafter	671
Total Lease Payments	796
Less: Imputed Interest	546
Total Finance Lease Liabilities	$ 250	$ 249