Leases (Lease Income Associated with Operating Leases) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Lessor, Lease, Description [Line Items]
Fixed payment	$ 17	$ 16
Variable payments	17	23
Total lease income under operating leases	34	39
Operating Revenues
Lessor, Lease, Description [Line Items]
Total lease income under operating leases	24	29
Other income
Lessor, Lease, Description [Line Items]
Total lease income under operating leases	$ 10	$ 10