Defined Benefit Pension and Other Postretirement Plans (Tables)

9 Months Ended

Jun. 30, 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 June 30,	2016			2015			2016			2015
Service cost	$	2.6		$	2.5		$	0.2		$	0.2
Interest cost	6.7			6.2			0.2			0.2
Expected return on assets	(8.0		)	(7.9		)	(0.2		)	(0.2		)
Amortization of:
Prior service cost (benefit)	—			—			(0.1		)	(0.2		)
Actuarial loss	2.7			2.5			—			0.1
Net benefit cost	4.0			3.3			0.1			0.1
Change in associated regulatory liabilities	—			—			0.9			0.9
Net expense	$	4.0		$	3.3		$	1.0		$	1.0
	Pension Benefits						Other Postretirement Benefits
Nine Months Ended June 30,	2016			2015			2016			2015
Service cost	$	7.6		$	7.4		$	0.6		$	0.5
Interest cost	19.9			18.8			0.7			0.6
Expected return on assets	(24.0		)	(23.8		)	(0.5		)	(0.5		)
Amortization of:
Prior service cost (benefit)	0.2			0.2			(0.4		)	(0.4		)
Actuarial loss	8.1			7.5			—			0.1
Net benefit cost	11.8			10.1			0.4			0.3
Change in associated regulatory liabilities	—			—			2.6			2.8
Net expense	$	11.8		$	10.1		$	3.0		$	3.1