Share-Based Compensation, Stock Options (Details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Exercised, number of shares	(46,100)	(54,209)	(141,728)
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
Contractual term (years)	10 years
Expected dividend yield	1.19%	0.88%	0.00%
Expected volatility	45.57%	46.12%	46.59%
Risk-free interest rate	1.96%	1.11%	0.46%
Expected term (years)	6 years	6 years	6 years
Weighted-average grant date fair value of stock options granted	38.31	40.05	29.45
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Options outstanding, number of shares, beginning of period	362,759
Options, weighted-average exercise price per share, beginning of period	54.94
Granted, number of shares	53,021
Granted, weighted-average exercise price	94.23
Exercised, number of shares	(46,100)
Exercised, weighted-average exercise price per share	43.93
Forfeited or expired, number of shares	(13,582)
Forfeited or expired, weighted-average exercise price per share	91.32
Options outstanding, number of shares, end of period	356,098	362,759
Options, weighted-average exercise price per share, end of period	60.83	54.94
Options outstanding, weighted-average remaining contractual term	6 years 6 months 29 days
Options outstanding, aggregate intrinsic value	21.8
Vested and expected to vest, number of shares	353,769
Vested and expected to vest, weighted-average exercise price per share	60.64
Vested and expected to vest, weighted-average remaining contractual term	6 years 6 months 25 days
Vested and expected to vest, aggregate intrinsic value	21.7
Exercisable, number of shares	256,888
Exercisable, weighted-average exercise price per share	49.62
Exercisable, weighted-average remaining contractual term	5 years 10 months 17 days
Exercisable, aggregate intrinsic value	18.6
Compensation expense	1.7	2.4	1.8
Income tax benefit recognized in the income statement	0.7	0.9	0.7
Aggregate grant-date fair value of stock options vested	2.3	1.8	1.3
Intrinsic value of stock options exercised	3.3	5.0	12.1
Cash received from option exercises	2.0	1.5	1.9
Tax benefit realized from options exercised during the annual period	1.3	1.9	4.6
Unrecognized compensation cost relating to nonvested stock options	1.0
Unrecognized compensation cost weighted-average period of recognition	12 months
Shares available for future grants	1,059,927