Lease Obligations - Lessee - Undiscounted Cash Flows (Details) $ in Millions	Mar. 31, 2020 USD ($)
Operating leases
Remainder of 2020	$ 67
2021	82
2022	78
2023	69
2024	61
2025	54
Thereafter	236
Total undiscounted cash flows	647
Less: Difference between undiscounted cash flows and discounted cash flows	94
Operating lease liabilities	553
Finance leases
Remainder of 2020	5
2021	6
2022	6
2023	2
2024	3
2025	3
Thereafter	38
Total undiscounted cash flows	63
Less: Difference between undiscounted cash flows and discounted cash flows	17
Finance lease liabilities	46
Lease Liabilities Payments Due [Abstract]
Remainder of 2020	72
2021	88
2022	84
2023	71
2024	64
2025	57
Thereafter	274
Total undiscounted cash flows	710
Less: Difference between undiscounted cash flows and discounted cash flows	111
Total lease liabilities	$ 599