Defined Benefit Pension and Other Postretirement Plans (Tables)

6 Months Ended

Mar. 31, 2017

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,	2017			2016			2017			2016
Service cost	$	3.0		$	2.5		$	0.3		$	0.2
Interest cost	6.1			6.6			0.2			0.3
Expected return on assets	(8.3		)	(8.0		)	(0.1		)	(0.1		)
Amortization of:
Prior service cost (benefit)	—			0.1			(0.2		)	(0.2		)
Actuarial loss	4.2			2.7			—			—
Net benefit cost	5.0			3.9			0.2			0.2
Change in associated regulatory liabilities	—			—			(0.1		)	0.8
Net benefit cost after change in regulatory liabilities	$	5.0		$	3.9		$	0.1		$	1.0
	Pension Benefits						Other Postretirement Benefits
Six Months Ended March 31,	2017			2016			2017			2016
Service cost	$	6.0		$	5.0		$	0.5		$	0.4
Interest cost	12.3			13.2			0.4			0.5
Expected return on assets	(16.6		)	(16.0		)	(0.3		)	(0.3		)
Amortization of:
Prior service cost (benefit)	0.1			0.2			(0.3		)	(0.3		)
Actuarial loss	8.3			5.4			0.1			—
Net benefit cost	10.1			7.8			0.4			0.3
Change in associated regulatory liabilities	—			—			(0.2		)	1.7
Net benefit cost after change in regulatory liabilities	$	10.1		$	7.8		$	0.2		$	2.0