Leases (Components of lease expense) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Leases [Abstract]
Operating lease costs	$ 12	$ 12	$ 37	$ 36
Variable lease costs	12	14	36	40
Total lease cost	$ 24	$ 26	$ 73	$ 76