Leases - Maturity of Lease Liabilities (Details) $ in Millions	Sep. 30, 2019 USD ($)
Operating Leases
The remainder of 2020	$ 206
2021	418
2022	355
2023	296
2024	242
Thereafter	901
Total lease payments	2,418
Less imputed interest	(293)
Present value of lease liabilities	2,125
Finance Leases
The remainder of 2020	8
2021	17
2022	17
2023	16
2024	15
Thereafter	125
Total lease payments	198
Less imputed interest	(42)
Present value of lease liabilities	156
Total
The remainder of 2020	214
2021	435
2022	372
2023	312
2024	257
Thereafter	1,026
Total lease payments	2,616
Less imputed interest	(335)
Present value of lease liabilities	2,281
Minimum sublease income under future noncancelable leases	$ 170