Leases (Lease Income Associated with Operating Leases) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Lessor, Lease, Description [Line Items]
Fixed payments	$ 13	$ 14	$ 42	$ 43
Variable payments	55	43	90	82
Total lease income under operating leases	68	57	132	125
Operating revenues
Lessor, Lease, Description [Line Items]
Total lease income under operating leases	26	26	70	74
Other income
Lessor, Lease, Description [Line Items]
Total lease income under operating leases	$ 42	$ 31	$ 62	$ 51