Stock Based Compensation (Details 3) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Additional disclosures
Stock based compensation expense	$ 51.8	$ 33.5	$ 39.5
Stock Appreciation Rights
Stock-Based Compensation arrangements
Contractual term	7 years
Graded vesting rights	3 years
Vesting rights	one-third of the award becoming exercisable each year on the anniversary date of the grant
Shares
Outstanding at the beginning of the period (in shares)	1,722,444	2,576,260	2,942,600
Granted (in shares)		240,884	383,000
Exercised (in shares)	(1,054,680)	(1,094,700)	(749,340)
Outstanding at the end of the period (in shares)	667,764	1,722,444	2,576,260
Exercisable at the end of the period (in shares)	386,582	1,145,972	1,805,328
Weighted-Average Exercise Price (in dollars per share)
Outstanding at the beginning of the period (in dollars per share)	$ 9.75	$ 8.02	$ 7.64
Granted (in dollars per share)		$ 17.59	$ 10.19
Exercised (in dollars per share)	$ 7.92	$ 7.42	$ 7.61
Outstanding at the end of the period (in dollars per share)	$ 12.63	$ 9.75	$ 8.02
Exercisable (in dollars per share)	$ 11.33	$ 7.97	$ 7.57
Additional disclosures
Aggregate intrinsic value of stock appreciation rights outstanding	17.4
Weighted-average remaining contractual term of non-vested shares	4 years 3 months 18 days
Aggregate intrinsic value of stock appreciation rights exercisable	10.6
Stock appreciation rights exercisable, weighted average remaining contractual term	4 years 1 month 6 days
Stock based compensation expense	0.3	1.9	2.1
Compensation expenses related to the immediate expensing of shares granted to retirement-eligible employees		1.2	0.1
Unamortized compensation expense	$ 0.1
Unrecognized compensation expense recognition period	1 year
Weighted-average value per SAR granted during the period (in dollars per share)		$ 8.16	$ 4.74
Assumptions
Stock price volatility (as a percent)		55.30%	52.70%
Risk free rate of return (as a percent)		0.90%	2.30%
Expected dividend yield (as a percent)		0.30%	0.30%
Expected term		5 years	5 years