Lease Obligations - Lessee - Other Information (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Leases [Abstract]
Operating leases, weighted average remaining lease term	9 years 2 months 19 days
Finance leases, weighted average remaining lease term	11 years 11 months 8 days
Operating leases, weighted average discount rate	3.10%
Finance leases, weighted average discount rate	2.36%
Cash paid for amounts included in the measurement of lease liabilities:(a)
Operating cash flows from operating leases	$ 69	$ 72
Operating cash flows from finance leases	2	1
Financing cash flows from finance leases	8	3
Gains on sale and leaseback transactions	$ 0	$ 5