Share Repurchase Program (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Number of shares repurchased	31.8	32.7
Aggregated cost, including fees	$ 481.8	$ 350.5	$ 400.8
Average price per share, including fees	$ 15.17	$ 10.72
2013 Share Repurchase Program
Share repurchase program, initial authorized amount	300.0
Share repurchase program, increased authorized amount	500.0
Stock Repurchase Program, Remaining Authorized Repurchase Amount	118.6
2012 Share Repurchase Program
Share repurchase program, initial authorized amount	300.0
Share repurchase program, increased authorized amount	$ 400.0