Leases (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Leases [Line Items]
Option to terminate leases, Lessee				1 year
Option to terminate leases, Lessor				1 year
Lease revenue	$ 17		$ 18	$ 52	$ 55
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