Earnings Per Share Data (Details) (USD $) In Millions, except Share data in Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Earnings Per Share Reconciliation [Abstract]
Net income available to common stockholders for purposes of computing basic earnings per share	$ 138.0	$ 118.3	$ 361.4	$ 237.4
Net income available to common stockholders for purposes of computing diluted earnings per share	$ 138.0	$ 118.3	$ 361.4	$ 237.4
Weighted-Average Number of Shares Outstanding Reconciliation [Abstract]
Basic shares	110,182	110,003	110,141	109,956
Effect of dilution	259	370	271	361
Diluted shares	110,441	110,373	110,412	110,317
Earnings Per Share [Abstract]
Basic earnings per share	$ 1.25	$ 1.08	$ 3.28	$ 2.16
Diluted earnings per share	$ 1.25	$ 1.07	$ 3.27	$ 2.15
Stock Options [Member]
Potentially Dilutive Shares Excluded from the Calculation [Abstract]
Stock options excluded as their inclusion would be anti-dilutive	0	0	76	74