Lease Obligations - Lessee - Other Information (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Leases [Abstract]
Operating leases, weighted average remaining lease term	9 years 4 months 17 days
Finance leases, weighted average remaining lease term	11 years 5 months 4 days
Operating leases, weighted average discount rate	3.12%
Finance leases, weighted average discount rate	2.25%
Cash paid for amounts included in the measurement of lease liabilities:(a)
Operating cash flows from operating leases	$ 47	$ 47
Operating cash flows from finance leases	1	1
Financing cash flows from finance leases	$ 2	$ 2