Share-Based Compensation Plans - Schedule of Valuation Assumptions for Non-Qualified Stock Options (Details) - Non-qualified Stock Options $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) grant_date $ / shares shares	Dec. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2015 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	1.95%	1.67%	1.61%
Dividend yield	0.18%	0.16%	0.12%
Volatility factor	27.45%	28.59%	26.80%
Expected term	5 years	5 years	5 years
Number of options granted (in shares) | shares	153,700	228,500	158,200
Weighted average grant date fair value (in dollars per share) | $ / shares	$ 17.47	$ 15.10	$ 19.90
Total intrinsic value of options exercised | $	$ 1.7	$ 3.5	$ 15.1
Number of grant dates | grant_date	2