Benefit Plans (Tables)

3 Months Ended

Mar. 31, 2016

Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Abstract]

Schedule of Components of Net Periodic Benefit Cost

The components of net periodic benefit cost for the three months ended March 31 were as follows ($ in millions):

	Pension benefits						Other retirement benefits						Total
	2016			2015			2016			2015			2016			2015
Service cost	$	2.7		$	2.7		$	0.1		$	0.1		$	2.8		$	2.8
Interest cost	2.6			3.9			0.1			0.1			2.7			4.0
Expected return on assets	(3.2		)	(5.7		)	—			—			(3.2		)	(5.7		)
Amortization of prior service credit	(0.3		)	(0.3		)	—			—			(0.3		)	(0.3		)
Recognized actuarial losses (gains)	1.1			1.6			(0.3		)	(0.3		)	0.8			1.3
Net periodic benefit cost	$	2.9		$	2.2		$	(0.1	)	$	(0.1	)	$	2.8		$	2.1

	Pension benefits				Other retirement benefits						Total
	2016		2015		2016			2015			2016		2015
U.S. plans	$	2.3	$	1.5	$	(0.1	)	$	(0.1	)	$	2.2	$	1.4
International plans	0.6		0.7		—			—			0.6		0.7
Net periodic benefit cost	$	2.9	$	2.2	$	(0.1	)	$	(0.1	)	$	2.8	$	2.1