Leases (Components of Lease Expense) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Leases [Abstract]
Operating lease costs	$ 12	$ 12	$ 35	$ 37
Variable lease costs	12	12	37	36
Total lease cost	$ 24	$ 24	$ 72	$ 73