Leases (Lease Income Associated with Operating Leases) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Lessor, Lease, Description [Line Items]
Fixed payments	$ 66	$ 65
Variable payments	124	128
Total lease income under operating leases	190	193
Operating Revenues
Lessor, Lease, Description [Line Items]
Total lease income under operating leases	108	130
Other Income
Lessor, Lease, Description [Line Items]
Total lease income under operating leases	$ 82	$ 63