Leasing Leasing (Lease, Cost) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Leases [Abstract]
Operating lease expense	$ 12	$ 11	$ 23	$ 21
Variable lease expense	2	1	4	3
Total lease expense, net	$ 14	$ 12	$ 27	$ 24