Leases (Components of Lease Expense) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Leases [Abstract]
Depreciation of right-of-use assets	$ 15	$ 11
Interest on lease liabilities	7	12
Total financing lease expense	22	23
Operating lease expense	133	110	$ 156
Variable lease expense	41	38
Short-term lease expense	4	5
Total lease expense	$ 200	$ 176