Defined Benefit Pension and Other Postretirement Plans (Tables)

6 Months Ended

Mar. 31, 2015

Defined Benefit Pension Plans and Defined Benefit Postretirement Plans Disclosure [Abstract]

Components of Net Periodic Pension Expense and Other Postretirement Benefit Costs

Net periodic pension expense and other postretirement benefit costs include the following components:

	Pension Benefits						Other Postretirement Benefits
Three Months Ended March 31,	2015			2014			2015			2014
Service cost	$	2.5		$	2.3		$	0.1		$	0.1
Interest cost	6.3			6.5			0.2			0.2
Expected return on assets	(8.0		)	(7.3		)	(0.1		)	(0.1		)
Amortization of:
Prior service cost (benefit)	0.1			0.1			(0.1		)	(0.1		)
Actuarial loss	2.5			1.9			—			—
Net benefit cost	3.4			3.5			0.1			0.1
Change in associated regulatory liabilities	—			—			1.0			0.9
Net expense	$	3.4		$	3.5		$	1.1		$	1.0
	Pension Benefits						Other Postretirement Benefits
Six Months Ended March 31,	2015			2014			2015			2014
Service cost	$	4.9		$	4.7		$	0.3		$	0.3
Interest cost	12.6			12.9			0.4			0.5
Expected return on assets	(15.9		)	(14.7		)	(0.3		)	(0.3		)
Amortization of:
Prior service cost (benefit)	0.2			0.2			(0.2		)	(0.2		)
Actuarial loss	5.0			3.8			—			—
Net benefit cost	6.8			6.9			0.2			0.3
Change in associated regulatory liabilities	—			—			1.9			1.8
Net expense	$	6.8		$	6.9		$	2.1		$	2.1