Defined Benefit Pension and Other Postretirement Plans (Tables)

6 Months Ended

Mar. 31, 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 March 31,	2018			2017			2018			2017
Service cost	$	2.8		$	3.0		$	0.2		$	0.3
Interest cost	6.5			6.1			0.2			0.2
Expected return on assets	(8.6		)	(8.3		)	(0.2		)	(0.1		)
Amortization of:
Prior service cost (benefit)	0.1			—			—			(0.2		)
Actuarial loss	3.3			4.2			—			—
Net benefit cost	4.1			5.0			0.2			0.2
Change in associated regulatory liabilities	—			—			(0.1		)	(0.1		)
Net benefit cost after change in regulatory liabilities	$	4.1		$	5.0		$	0.1		$	0.1
	Pension Benefits						Other Postretirement Benefits
Six Months Ended March 31,	2018			2017			2018			2017
Service cost	$	5.6		$	6.0		$	0.4		$	0.5
Interest cost	13.0			12.3			0.4			0.4
Expected return on assets	(17.2		)	(16.6		)	(0.4		)	(0.3		)
Amortization of:
Prior service cost (benefit)	0.2			0.1			(0.1		)	(0.3		)
Actuarial loss	6.6			8.3			—			0.1
Net benefit cost	8.2			10.1			0.3			0.4
Change in associated regulatory liabilities	—			—			(0.2		)	(0.2		)
Net benefit cost after change in regulatory liabilities	$	8.2		$	10.1		$	0.1		$	0.2