Leases (Narrative) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019 USD ($)
Leases [Line Items]
Option to terminate leases, Lessee	1 year
Option to terminate leases, Lessor	1 year
Lease revenue	$ 18
Accounting Standards Update 2016-02 [Member]
Leases [Line Items]
Impact of adoption of new accounting principle	11
Cumulative-effect adjustment, Net of tax	11
Accounting Standards Update 2018-11 [Member]
Leases [Line Items]
Impact of adoption of new accounting principle	$ 15
Minimum [Member]
Leases [Line Items]
Operating and finace lease terms, Lessee	1 year
Operator lease terms, Lessor	1 year
Maximum [Member]
Leases [Line Items]
Operating and finace lease terms, Lessee	99 years
Operator lease terms, Lessor	99 years