Defined Benefit Pension and Other Postretirement Plans (Tables)

9 Months Ended

Jun. 30, 2018

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,	2018			2017			2018			2017
Service cost	$	2.8		$	3.0		$	0.2		$	0.3
Interest cost	6.5			6.2			0.3			0.2
Expected return on assets	(8.7		)	(8.4		)	(0.2		)	(0.2		)
Amortization of:
Prior service cost (benefit)	—			0.1			—			(0.2		)
Actuarial loss	3.4			4.2			—			0.1
Net benefit cost	4.0			5.1			0.3			0.2
Change in associated regulatory liabilities	—			—			(0.1		)	(0.1		)
Net benefit cost after change in regulatory liabilities	$	4.0		$	5.1		$	0.2		$	0.1
	Pension Benefits						Other Postretirement Benefits
Nine Months Ended June 30,	2018			2017			2018			2017
Service cost	$	8.4		$	9.0		$	0.6		$	0.7
Interest cost	19.5			18.5			0.7			0.6
Expected return on assets	(25.9		)	(25.0		)	(0.6		)	(0.5		)
Amortization of:
Prior service cost (benefit)	0.2			0.2			(0.2		)	(0.5		)
Actuarial loss	10.0			12.5			—			0.2
Net benefit cost	12.2			15.2			0.5			0.5
Change in associated regulatory liabilities	—			—			(0.4		)	(0.4		)
Net benefit cost after change in regulatory liabilities	$	12.2		$	15.2		$	0.1		$	0.1