Income Taxes (Reconciliation of Beginning and Ending Unrecognized Tax Benefits) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reconciliation of Unrecognized Tax Benefits
Balance at beginning of year	$ 64	$ 85	$ 66
Additions for tax positions of prior years	12	32	22
Reductions for tax positions of prior years	(2)	(16)	(1)
Tax settlements	0	(37)	(2)
Balance at end of year	$ 74	$ 64	$ 85