Lease Obligations - Lessee - Undiscounted Cash Flows (Details) $ in Millions	Dec. 31, 2019 USD ($)
Operating leases
2020	$ 90
2021	81
2022	76
2023	67
2024	58
Thereafter	280
Total undiscounted cash flows	652
Less: difference between undiscounted cash flows and discounted cash flows	97
Operating lease liabilities	555
Finance leases
2020	6
2021	5
2022	5
2023	2
2024	2
Thereafter	26
Total undiscounted cash flows	46
Less: Difference between undiscounted cash flows and discounted cash flows	11
Finance lease liabilities	35
Lease Liabilities Payments Due [Abstract]
2020	96
2021	86
2022	81
2023	69
2024	60
Thereafter	306
Total undiscounted cash flows	698
Less: Difference between undiscounted cash flows and discounted cash flows	108
Total lease liabilities	$ 590