Defined Benefit Pension and Other Postretirement Plans (Tables)

9 Months Ended

Jun. 30, 2017

Retirement Benefits [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,	2017			2016			2017			2016
Service cost	$	3.0		$	2.6		$	0.3		$	0.2
Interest cost	6.2			6.7			0.2			0.2
Expected return on assets	(8.4		)	(8.0		)	(0.2		)	(0.2		)
Amortization of:
Prior service cost (benefit)	0.1			—			(0.2		)	(0.1		)
Actuarial loss	4.2			2.7			0.1			—
Net benefit cost	5.1			4.0			0.2			0.1
Change in associated regulatory liabilities	—			—			(0.1		)	0.9
Net benefit cost after change in regulatory liabilities	$	5.1		$	4.0		$	0.1		$	1.0
	Pension Benefits						Other Postretirement Benefits
Nine Months Ended June 30,	2017			2016			2017			2016
Service cost	$	9.0		$	7.6		$	0.7		$	0.6
Interest cost	18.5			19.9			0.6			0.7
Expected return on assets	(25.0		)	(24.0		)	(0.5		)	(0.5		)
Amortization of:
Prior service cost (benefit)	0.2			0.2			(0.5		)	(0.4		)
Actuarial loss	12.5			8.1			0.2			—
Net benefit cost	15.2			11.8			0.5			0.4
Change in associated regulatory liabilities	—			—			(0.4		)	2.6
Net benefit cost after change in regulatory liabilities	$	15.2		$	11.8		$	0.1		$	3.0