Stock-Based Compensation Plans (Summary of Stock Option Activity) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Employee Stock Option Plan
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Shares, Outstanding at Beginning of Year	17,829	18,000	17,722
Shares, Granted	2,966	5,757	5,462
Shares, Exercised	(2,344)	(5,224)	(4,450)
Shares, Forfeited	(759)	(704)	(734)
Shares, Outstanding at End of Year	17,692	17,829	18,000
Shares, Exercisable at End of Year	6,858	4,564	5,490
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Wtd. Avg. Ex. Price, Outstanding at Beginning of Year (usd per share)	$ 13	$ 12	$ 11
Wtd. Avg. Ex. Price, Granted (usd per share)	17	15	13
Wtd. Avg. Ex. Price, Exercised (usd per share)	12	11	8
Wtd. Avg. Ex. Price, Forfeited (usd per share)	14	13	12
Wtd. Avg. Ex. Price, Outstanding at End of Year (usd per share)	14	13	12
Wtd. Avg. Ex. Price, Exercisable at End of Year (usd per share)	$ 13	$ 12	$ 12
Option expiration period, years	3 years	3 years 6 months	3 years 4 months 24 days
Wtd. Avg. Remaining Contract Life, Exercisable at End of Year	2 years 1 month 6 days	2 years 3 months 18 days	2 years 3 months 18 days
Aggregate Intrinsic Value, Exercised	$ 11,596	$ 26,618	$ 20,884
Aggregate Intrinsic Value, Outstanding at End of Year	45,842	90,759	85,633
Aggregate Intrinsic Value, Exercisable at End of Year	$ 23,917	$ 28,342	$ 28,302
Non-Employee Director Stock Option Plan
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Shares, Outstanding at Beginning of Year	381	462	468
Shares, Granted	49	98	84
Shares, Exercised	(57)	(167)	(90)
Shares, Forfeited	0	(12)	0
Shares, Outstanding at End of Year	373	381	462
Shares, Exercisable at End of Year	373	381	462
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Wtd. Avg. Ex. Price, Outstanding at Beginning of Year (usd per share)	$ 12	$ 11	$ 11
Wtd. Avg. Ex. Price, Granted (usd per share)	17	14	12
Wtd. Avg. Ex. Price, Exercised (usd per share)	11	10	10
Wtd. Avg. Ex. Price, Forfeited (usd per share)	0	16	0
Wtd. Avg. Ex. Price, Outstanding at End of Year (usd per share)	13	12	11
Wtd. Avg. Ex. Price, Exercisable at End of Year (usd per share)	$ 13	$ 12	$ 11
Option expiration period, years	6 years 4 months 24 days	6 years 8 months 12 days	6 years 4 months 24 days
Wtd. Avg. Remaining Contract Life, Exercisable at End of Year	6 years 4 months 24 days	6 years 8 months 12 days	6 years 4 months 24 days
Aggregate Intrinsic Value, Exercised		$ 893	$ 300
Aggregate Intrinsic Value, Outstanding at End of Year	$ 1,069	2,137	2,491
Aggregate Intrinsic Value, Exercisable at End of Year	$ 1,069	$ 2,137	$ 2,491