Leases (Components of lease expense) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Leases [Abstract]
Operating lease costs	$ 12	$ 12	$ 24	$ 24
Variable lease costs	12	13	24	26
Total lease cost	$ 24	$ 25	$ 48	$ 50