Stock Option Activity (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Stock options outstanding as of January 1, 2012	14.1
Granted	0.7
Exercised	(5.2)	(1.2)	(1.3)
Cancelled/expired	(0.1)
Forfeited	(0.1)
Stock options outstanding as of December 31, 2012	9.4	14.1
Stock options outstanding as of Jan 1, 2012, Weighted-average exercise price	$ 9.76
Granted, Weighted-average exercise price	$ 12.79
Exercised, Weighted-average exercise price	$ 9.25
Cancelled/expired, Weighted-average exercise price	$ 12.34
Forfeited, Weighted-average exercise price	$ 5.35
Stock options outstanding as of Dec 31, 2012, Weighted-average exercise price	$ 10.24	$ 9.76
Stock options outstanding, Weighted-average remaining contractual term	4 years 5 months
Stock options outstanding, Aggregate intrinsic value	$ 70.0
Stock options vested and expected to vest, Outstanding	9.4
Stock options vested and expected to vest, Weighted-average exercise price	$ 10.24
Stock options vested and expected to vest, Weighted-average remaining contractual term	4 years 5 months
Stock options vested and expected to vest, Aggregate intrinsic value	69.8
Stock options exercisable, Number	7.9
Stock options exercisable, Weighted-average exercise price	$ 9.92
Stock options exercisable, Weighted-average remaining contractual term	3 years 7 months
Stock options exercisable, Aggregate intrinsic value	61.3
Non-vested as of January 1, 2012	3.9
Granted	0.7
Vested	(3.0)
Forfeited	(0.1)
Non-vested as of December 31, 2012	1.5	3.9
Non-vested as of January 1, 2012, Weighted-average grant date fair value	$ 3.29
Granted, Weighted-average grant date fair value	$ 4.14	$ 4.24	$ 4.57
Vested, Weighted-average grant date fair value	$ 3.02
Forfeited, Weighted-average grant date fair value	$ 3.01
Non-vested as of December 31, 2012, Weighted-average grant date fair value	$ 4.21	$ 3.29
Non-vested options outstanding, Weighted-average remaining contractual term	8 years 2 months
Non-vested options outstanding, Aggregate intrinsic value	8.6
Intrinsic value of stock options exercised	26.2	2.0	3.2
Proceeds from Stock Options Exercised including Taxes Withheld	$ 59.5	$ 11.7	$ 13.3