Leases (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2019
Leases [Line Items]
Option to terminate leases, Lessee			1 year
Option to terminate leases, Lessor			1 year
Lease revenue	$ 17		$ 35
Accounting Standards Update 2016-02 [Member]
Leases [Line Items]
Impact of adoption of new accounting principle		$ 11	11
Cumulative-effect adjustment, Net of tax		$ 11	11
Accounting Standards Update 2018-11 [Member]
Leases [Line Items]
Impact of adoption of new accounting principle			11
Cumulative-effect adjustment, Net of tax			$ 11
Minimum [Member]
Leases [Line Items]
Operating and finace lease terms, Lessee			1 year
Operator lease terms, Lessor	1 year		1 year
Maximum [Member]
Leases [Line Items]
Operating and finace lease terms, Lessee			99 years
Operator lease terms, Lessor	99 years		99 years