Stock Compensation Plans - Option Activity (Details) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding - Number of Shares | shares	3,783,497
Outstanding - beginning of year, Weighted Average Exercise Price | $ / shares	$ 34.41
Granted, Number of Shares | shares	484,186
Granted, Weighted Average-exercise Price | $ / shares	$ 45.43
Exercised, Number of Shares | shares	(1,053,189)
Exercised, Weighted-average Exercise Price | $ / shares	$ 32.62
Canceled or expired, Number of Shares | shares	(63,373)
Canceled or expired, Weighted-average Exercise Price | $ / shares	$ 36.94
Outstanding - Number of Shares | shares	3,151,121
Outstanding - end of year, Weighted Average Exercise Price | $ / shares	$ 36.65
Outstanding - end of year, Weighted-average Remaining Contractual Term	6 years
Outstanding - end of year, Aggregate Intrinsic Value | $	$ 39.4
Option expected to vest, Number of Shares | shares	3,151,121
Option expected to vest, Weighted-average Exercise Price | $ / shares	$ 36.65
Option expected to vest, Weighted-average Remaining Contractual Term	6 years
Option expected to vest, Aggregate Intrinsic Value | $	$ 39.4
Options exercisable, Number of Shares | shares	1,859,277
Options exercisable, Weighted-average Exercise Price | $ / shares	$ 36.05
Options exercisable, Weighted-average Remaining Contractual Term, Exercisable	5 years
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value | $	$ 24.4