Leases - Future Minimum Lease Payments Due Under ASC 842 Guidance (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Operating Leases
2020	$ 302
2021	261
2022	212
2023	163
2024	136
Thereafter	790
Total future lease payments	1,864
Less imputed interest	361
Present value of future lease payments	1,503
Less current portion of lease liabilities	252	$ 0
Long-term lease liabilities	1,251	$ 0
ROU assets	1,432
Finance Leases
2020	91
2021	83
2022	83
2023	36
2024	19
Thereafter	131
Total future lease payments	443
Less imputed interest	89
Present value of future lease payments	354
Less current portion of lease liabilities	67
Long-term lease liabilities	287
ROU assets	$ 391