Net Income Per Share (Tables)

6 Months Ended

Jun. 30, 2013

Earnings Per Share [Abstract]

Net income and shares used in basic and diluted net income per share

The following table reconciles net income and shares used in the calculation of basic net income per share to those used for diluted net income per share:

	Three Months Ended June 30,				Six Months Ended June 30,
($ in millions)	2013		2012		2013		2012
Net income, as reported, for basic net income per share	$	30.2	$	15.6	$	61.9	$	44.8
Plus: interest expense on convertible debt, net of tax	—		0.8		—		1.9
Net income for diluted net income per share	$	30.2	$	16.4	$	61.9	$	46.7
Weighted average common shares outstanding	34.7		34.0		34.6		33.9
Assumed stock options exercised and awards vested, based on the treasury stock method	0.7		0.5		0.6		0.5
Assumed conversion of convertible debt, based on the if-converted method	—		2.1		0.1		2.5
Weighted average shares assuming dilution	35.4		36.6		35.3		36.9