Earnings Per Share (Tables)

12 Months Ended

Dec. 31, 2014

Earnings Per Share [Abstract]

Reconciliation of Basic Earnings Per Share Computation to the Diluted Earnings Per Share Computation

The following table reconciles the basic earnings per share computation to the diluted earnings per share computation (in millions, except share and per share amounts):

	2014		2013		2012
Net income available to common stockholders for purposes of computing basic and diluted earnings per share	$	502.4	$	351.2	$	377.1
Weighted-average number of shares outstanding (in thousands):
Basic shares	110,163		109,973		109,712
Effect of dilution	270		367		368
Diluted shares	110,433		110,340		110,080
Earnings per share:
Basic earnings per share	$	4.56	$	3.19	$	3.44
Diluted earnings per share	$	4.55	$	3.18	$	3.43
Potentially dilutive shares excluded from the calculation (in thousands):	2014		2013		2012
Stock options excluded as their inclusion would be anti-dilutive	57		57		—