Leases (Lease Income Associated with Operating Leases) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Lessor, Lease, Description [Line Items]
Fixed payments	$ 16	$ 17	$ 33	$ 33
Variable payments	18	16	35	39
Total lease income under operating leases	34	33	68	72
Operating revenues
Lessor, Lease, Description [Line Items]
Total lease income under operating leases	24	23	48	52
Other income
Lessor, Lease, Description [Line Items]
Total lease income under operating leases	$ 10	$ 10	$ 20	$ 20