Treasury Stock Transactions (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Equity, Class of Treasury Stock [Line Items]
Number of Treasury Shares Repurchased	8.7	11.2	23.6
Cost of Shares Repurchased	$ 300.6	$ 318.6	$ 500.6
Commission Paid on Stock Repurchases	0.1	0.2	0.6
Repurchase Program Authorized in December 2013
Equity, Class of Treasury Stock [Line Items]
Authorized Amount of Treasury Share Repurchases Under Stock Repurchase Program	750.0
Remaining Amount of Treasury Share Repurchases Authorized Under Stock Repurchase Program	429.5
Repurchase Program Authorized in July 2012
Equity, Class of Treasury Stock [Line Items]
Authorized Amount of Treasury Share Repurchases Under Stock Repurchase Program	750.0
Remaining Amount of Treasury Share Repurchases Authorized Under Stock Repurchase Program	0
Repurchase Program Authorized in February 2011
Equity, Class of Treasury Stock [Line Items]
Authorized Amount of Treasury Share Repurchases Under Stock Repurchase Program	1,000.0
Remaining Amount of Treasury Share Repurchases Authorized Under Stock Repurchase Program	$ 0