Leases - Future Minimum Lease Payments Due Under ASC 842 Guidance (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Operating Leases
2019 (excluding the three months ended March 31, 2019)	$ 233
2020	253
2021	208
2022	161
2023	122
Thereafter	722
Total future lease payments	1,699
Less imputed interest	315
Present value of future lease payments	1,384
Less current portion of lease liabilities	255	$ 0
Long-term lease liabilities	1,129	$ 0
ROU assets	1,315
Finance Leases
2019 (excluding the three months ended March 31, 2019)	67
2020	81
2021	74
2022	74
2023	29
Thereafter	66
Total future lease payments	391
Less imputed interest	81
Present value of future lease payments	310
Less current portion of lease liabilities	66
Long-term lease liabilities	244
ROU assets	$ 357