Share-Based Compensation, Stock Options (Details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended						0 Months Ended	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Stock Options [Member]	Dec. 31, 2011 Stock Options [Member]	Dec. 31, 2010 Stock Options [Member]	Mar. 01, 2010 Stock Options [Member] Market-based Award [Member] Tranches days	Dec. 31, 2012 Stock Option and Performance Award Plan 2008 [Member]	Dec. 31, 2012 Stock Option and Performance Award Plan 1991 [Member]	Dec. 31, 2012 Minimum [Member] Stock Options [Member]	Dec. 31, 2012 Maximum [Member] Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Percentage of Closing Market Price								100.00%
Share-based Compensation Arrangement by Share-based Payment Award, Percentage of Average Market Price									100.00%
Vesting Period										3 years	5 years
Contractual term (years)				10 years
Number of tranches							3
Target price number one							$ 38.95
Target price number two							$ 42.85
Target price number three							$ 47.14
Market condition, number of trading days							30
Expected dividend yield				0.00%	0.00%	0.00%
Expected volatility				46.59%	45.40%	43.43%
Risk-free interest rate				0.46%	1.29%	2.83%
Expected term (years)				6 years	6 years	6 years 6 months
Weighted-average grant date fair value of stock options granted				$ 29.45	$ 23.39	$ 15.96
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Options outstanding, number of shares, beginning of period				501,636
Options, weighted-average exercise price per share, beginning of period				$ 29.81
Granted, number of shares				69,552			190,300
Granted, weighted-average exercise price				$ 66.99
Exercised, number of shares	(141,728)	(158,440)	(480,514)	(201,704)
Exercised, weighted-average exercise price per share				$ 17.12
Forfeited or expired, number of shares				(1,413)
Forfeited or expired, weighted-average exercise price per share				$ 59.87
Options outstanding, number of shares, end of period				368,071	501,636
Options, weighted-average exercise price per share, end of period				$ 43.67	$ 29.81
Options outstanding, weighted-average remaining contractual term				6 years 11 months 19 days
Options outstanding, aggregate intrinsic value				$ 14.7
Vested and expected to vest, number of shares				363,782
Vested and expected to vest, weighted-average exercise price per share				$ 43.55
Vested and expected to vest, weighted-average remaining contractual term				6 years 11 months 16 days
Vested and expected to vest, aggregate intrinsic value				14.5
Exercisable, number of shares				222,486
Exercisable, weighted-average exercise price per share				$ 34.43
Exercisable, weighted-average remaining contractual term				6 years 1 month 2 days
Exercisable, aggregate intrinsic value				10.9
Compensation expense				1.8	2.2	2.7
Income tax benefit recognized in the income statement				0.7	0.8	1.0
Aggregate grant-date fair value of stock options vested				1.3	1.1	2.0
Intrinsic value of stock options exercised				12.1	9.5	21.7
Cash received from option exercises				1.9	2.1	2.1
Tax benefit realized from options exercised during the annual period				4.6	0.2	1.2
Unrecognized compensation cost relating to nonvested stock options				$ 1.2
Unrecognized compensation cost weighted-average period of recognition				12 months
Shares available for future grants				1,331,896