Defined Benefit Pension and Other Postretirement Plans (Tables)

6 Months Ended

Mar. 31, 2016

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,	2016			2015			2016			2015
Service cost	$	2.5		$	2.5		$	0.2		$	0.1
Interest cost	6.6			6.3			0.3			0.2
Expected return on assets	(8.0		)	(8.0		)	(0.1		)	(0.1		)
Amortization of:
Prior service cost (benefit)	0.1			0.1			(0.2		)	(0.1		)
Actuarial loss	2.7			2.5			—			—
Net benefit cost	3.9			3.4			0.2			0.1
Change in associated regulatory liabilities	—			—			0.8			1.0
Net expense	$	3.9		$	3.4		$	1.0		$	1.1
	Pension Benefits						Other Postretirement Benefits
Six Months Ended March 31,	2016			2015			2016			2015
Service cost	$	5.0		$	4.9		$	0.4		$	0.3
Interest cost	13.2			12.6			0.5			0.4
Expected return on assets	(16.0		)	(15.9		)	(0.3		)	(0.3		)
Amortization of:
Prior service cost (benefit)	0.2			0.2			(0.3		)	(0.2		)
Actuarial loss	5.4			5.0			—			—
Net benefit cost	7.8			6.8			0.3			0.2
Change in associated regulatory liabilities	—			—			1.7			1.9
Net expense	$	7.8		$	6.8		$	2.0		$	2.1