Leases - Maturities of Lease Liabilities, Topic 842 (Details) $ in Millions	Mar. 31, 2020 USD ($)
Finance Leases
2021	$ 464
2022	339
2023	195
2024	81
2025	16
Thereafter	0
Total lease payments	1,095
Less: imputed interest	49
Finance lease liabilities	1,046
Real Estate
Operating Leases
2021	429
2022	330
2023	255
2024	189
2025	121
Thereafter	211
Total lease payments	1,535
Less: imputed interest	145
Total payments	1,390
Equipment
Operating Leases
2021	79
2022	41
2023	19
2024	11
2025	4
Thereafter	10
Total lease payments	164
Less: imputed interest	9
Total payments	$ 155