Stock-Based Compensation (Details 2) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2013 item	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Assumptions used in determining the estimated fair value of stock options
Dividends paid	$ 0	$ 0	$ 0
Non-qualified stock options
Summary of option activity
Vesting period	5 years 11 months 16 days	6 years 3 months 4 days	6 years 5 months 12 days	5 years 1 month 28 days
Expiration from date of grant	10 years
Outstanding at the beginning of the period	3.3	3.4	4.5
Options granted	0.3	0.5	0.6
Options exercised	(0.6)	(0.6)	(1.6)
Options expired or forfeited			(0.1)
Outstanding at the end of the period	3.0	3.3	3.4	4.5
Weighted-Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)	$ 15.67	$ 13.55	$ 10.84
Options granted (in dollars per share)	$ 28.27	$ 25.03	$ 19.19
Options exercised (in dollars per share)	$ 14.44	$ 10.41	$ 8.17
Options expired or forfeited (in dollars per share)		$ 21.82	$ 12.93
Outstanding at the end of the period (in dollars per share)	$ 17.30	$ 15.67	$ 13.55	$ 10.84
Weighted-Average Remaining Contractual Life
Weighted-Average Remaining Contractual Life	5 years 11 months 16 days	6 years 3 months 4 days	6 years 5 months 12 days	5 years 1 month 28 days
Other disclosures
Aggregate intrinsic value of outstanding options	82.5	37.4
Aggregate intrinsic value of exercisable options	66.9	29.5
Total intrinsic value of options exercised	10.9	9.1
Total number of options exercisable (in shares)	2.2	2.2
Weighted average exercise price of options exercisable (in dollars per share)	$ 14.09	$ 13.57
Total unrecognized compensation cost on nonvested options	$ 1.6	$ 2.1
Information about outstanding non-qualified stock options
Exercise price, low end of range (in dollars per share)	$ 7.83
Exercise price, high end of range (in dollars per share)	$ 28.27
Number of Options Outstanding	3.0
Weighted Average Remaining Life	5 years 11 months 16 days
Weighted average exercise price of options Outstanding (in dollars per share)	$ 17.30
Number of Options Exercisable (in shares)	2.2
Weighted average exercise price of options exercisable (in dollars per share)	$ 14.09
Assumptions used in determining the estimated fair value of stock options
Risk-free interest rate (as a percent)	1.08%	0.83%	1.88%
Expected option life, Executive	6 years 3 months 25 days	5 years 5 months 8 days	4 years 10 months 2 days
Expected option life, Non-Executive	4 years 9 months 18 days	4 years 5 months 12 days	4 years 8 months 16 days
Volatility (as a percent)	40.12%	45.76%	44.08%
Weighted-average fair value per option granted	$ 11.07	$ 10.24	$ 7.65
Period of historical option activity considered to determine expected option life	10 years
Number of separate employee groups	2
Non-qualified stock options | Minimum
Other disclosures
Period over which unrecognized compensation costs will be recognized	1 year
Non-qualified stock options | Maximum
Other disclosures
Period over which unrecognized compensation costs will be recognized	3 years
Non-qualified stock options | Range of exercise prices $7.83 - $10.90
Information about outstanding non-qualified stock options
Exercise price, low end of range (in dollars per share)	$ 7.83
Exercise price, high end of range (in dollars per share)	$ 10.90
Number of Options Outstanding	1.1
Weighted Average Remaining Life	5 years 7 months 2 days
Weighted average exercise price of options Outstanding (in dollars per share)	$ 9.38
Number of Options Exercisable (in shares)	1.1
Weighted average exercise price of options exercisable (in dollars per share)	$ 9.38
Non-qualified stock options | Range of exercise prices $14.51 - $21.11
Information about outstanding non-qualified stock options
Exercise price, low end of range (in dollars per share)	$ 14.51
Exercise price, high end of range (in dollars per share)	$ 21.11
Number of Options Outstanding	1.0
Weighted Average Remaining Life	4 years 11 months 19 days
Weighted average exercise price of options Outstanding (in dollars per share)	$ 18.54
Number of Options Exercisable (in shares)	0.8
Weighted average exercise price of options exercisable (in dollars per share)	$ 17.45
Non-qualified stock options | Range of exercise prices $22.00 - $28.27
Information about outstanding non-qualified stock options
Exercise price, low end of range (in dollars per share)	$ 22.00
Exercise price, high end of range (in dollars per share)	$ 28.27
Number of Options Outstanding	0.9
Weighted Average Remaining Life	7 years 6 months 29 days
Weighted average exercise price of options Outstanding (in dollars per share)	$ 25.79
Number of Options Exercisable (in shares)	0.3
Weighted average exercise price of options exercisable (in dollars per share)	$ 23.54