Benefit Plans (Tables)

9 Months Ended

Sep. 30, 2017

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 endedSeptember 30 were as follows ($ in millions):

	Pension benefits						Other retirement benefits						Total
	2017			2016			2017			2016			2017			2016
Service cost	$	2.5		$	2.3		$	—		$	0.1		$	2.5		$	2.4
Interest cost	2.4			2.7			—			0.1			2.4			2.8
Expected return on assets	(3.4		)	(3.1		)	—			—			(3.4		)	(3.1		)
Amortization of prior service credit	(0.3		)	(0.3		)	(0.1		)	—			(0.4		)	(0.3		)
Recognized actuarial losses (gains)	1.2			1.3			(0.9		)	(0.3		)	0.3			1.0
Net periodic benefit cost	$	2.4		$	2.9		$	(1.0	)	$	(0.1	)	$	1.4		$	2.8

	Pension benefits				Other retirement benefits						Total
	2017		2016		2017			2016			2017		2016
U.S. plans	$	1.7	$	2.3	$	(1.0	)	$	(0.1	)	$	0.7	$	2.2
International plans	0.7		0.6		—			—			0.7		0.6
Net periodic benefit cost	$	2.4	$	2.9	$	(1.0	)	$	(0.1	)	$	1.4	$	2.8

The components of net periodic benefit cost for the nine months endedSeptember 30 were as follows ($ in millions):

	Pension benefits						Other retirement benefits						Total
	2017			2016			2017			2016			2017			2016
Service cost	$	7.8		$	7.6		$	—		$	0.4		$	7.8		$	8.0
Interest cost	7.3			7.9			0.2			0.3			7.5			8.2
Expected return on assets	(10.1		)	(9.5		)	—			—			(10.1		)	(9.5		)
Amortization of transition obligation	—			0.1			—			—			—			0.1
Amortization of prior service credit	(1.0		)	(1.0		)	(0.5		)	—			(1.5		)	(1.0		)
Recognized actuarial losses (gains)	3.6			3.6			(2.0		)	(1.0		)	1.6			2.6
Net periodic benefit cost	$	7.6		$	8.7		$	(2.3	)	$	(0.3	)	$	5.3		$	8.4

	Pension benefits				Other retirement benefits						Total
	2017		2016		2017			2016			2017		2016
U.S. plans	$	5.5	$	6.9	$	(2.3	)	$	(0.3	)	$	3.2	$	6.6
International plans	2.1		1.8		—			—			2.1		1.8
Net periodic benefit cost	$	7.6	$	8.7	$	(2.3	)	$	(0.3	)	$	5.3	$	8.4