Income Taxes (Summary of Unrecognized Tax Benefits) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits — January 1	$ 129	$ 136	$ 130
Current year tax positions	0	3	0
Prior year tax positions			7
Prior year tax positions	(3)	(5)
Settlements	(12)	(5)	(1)
Unrecognized tax benefits — December 31	$ 114	$ 129	$ 136