Pension and Other Postretirement Benefits (Tables)

6 Months Ended

Oct. 31, 2011

Pension and Other Postretirement Benefits [Abstract]

Pension and other postretirement benefit expense

	Three Months Ended October 31,						Six Months Ended October 31,
(Dollars in millions)	2010			2011			2010			2011
Pension Benefits:
Service cost	$	3.9		$	4.0		$	7.8		$	8.0
Interest cost		8.3			8.5			16.7			17.0
Expected return on plan assets		(9.1	)		(10.0	)		(18.1	)		(20.1	)
Amortization of:
Prior service cost		0.2			0.2			0.4			0.4
Net actuarial loss		4.7			4.8			9.3			9.7
Net expense	$	8.0		$	7.5		$	16.1		$	15.0
Other Postretirement Benefits:
Service cost	$	0.3		$	0.4		$	0.6		$	0.7
Interest cost		0.8			0.7			1.6			1.5
Amortization of:
Prior service cost		—			0.2			—			0.3
Net actuarial loss		—			—			0.1			—
Net expense	$	1.1		$	1.3		$	2.3		$	2.5