Stock-Based Compensation Plans (Summary of Stock Option Activity) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Shares
Shares, Outstanding at Beginning of Year (in shares)	5,435	8,944	11,837
Shares, Granted (in shares)	1,571	1,049	1,613
Shares, Exercised (in shares)	(2,077)	(4,402)	(4,278)
Shares, Forfeited (in shares)	(396)	(156)	(228)
Shares, Outstanding at End of Year (in shares)	4,533	5,435	8,944
Shares, Exercisable at End of Year (in shares)	1,358	1,859	4,101
Wtd. Avg Grant Date Fair Value
Wtd. Avg. Ex. Price, Outstanding at Beginning of Year (in dollars per share)	$ 20	$ 18	$ 16
Wtd. Avg. Ex. Price, Granted (in dollars per share)	26	25	22
Wtd. Avg. Ex. Price, Exercised (in dollars per share)	18	16	15
Wtd. Avg. Ex. Price, Forfeited (in dollars per share)	22	20	18
Wtd. Avg. Ex. Price, Outstanding at End of Year (in dollars per share)	23	20	18
Wtd. Avg. Ex. Price, Exercisable at End of Year (in dollars per share)	$ 20	$ 18	$ 16
Option expiration period, years	3 years 4 months 24 days	3 years 1 month 6 days	2 years 9 months 18 days
Wtd. Avg. Remaining Contract Life, Exercisable at End of Year	2 years 3 months 18 days	2 years 2 months 12 days	1 year 8 months 12 days
Aggregate Intrinsic Value, Exercised	$ 23,861	$ 36,294	$ 38,097
Aggregate Intrinsic Value, Outstanding at End of Year	48,501	47,170	24,881
Aggregate Intrinsic Value, Exercisable at End of Year	$ 18,334	$ 20,484	$ 16,162