Defined Benefit Pension and Other Postretirement Plans (Tables)

9 Months Ended

Jun. 30, 2020

Retirement Benefits [Abstract]

Components of Net Periodic Pension Expense and Other Postretirement Benefit Costs

Net periodic pension cost and other postretirement benefit cost include the following components:

	Pension Benefits				Other Postretirement Benefits
Three Months Ended June 30,	2020		2019		2020		2019
Service cost	$	2.8	$	2.5	$	0.1	$	—
Interest cost	5.7		6.8		0.1		0.2
Expected return on assets	(9.4)		(9.0)		(0.2)		(0.2)
Amortization of:
Prior service cost (benefit)	0.1		0.1		(0.1)		(0.1)
Actuarial loss	3.8		1.9		—		—
Net cost (benefit)	3.0		2.3		(0.1)		(0.1)
Change in associated regulatory liabilities	—		—		(0.3)		(0.3)
Net cost (benefit) after change in regulatory liabilities	$	3.0	$	2.3	$	(0.4)	$	(0.4)
	Pension Benefits				Other Postretirement Benefits
Nine Months Ended June 30,	2020		2019		2020		2019
Service cost	$	8.4	$	7.6	$	0.2	$	0.1
Interest cost	17.3		20.4		0.4		0.5
Expected return on assets	(28.2)		(27.1)		(0.6)		(0.6)
Curtailment gain	(1.1)		—		—		—
Amortization of:
Prior service cost (benefit)	0.2		0.2		(0.3)		(0.3)
Actuarial loss (gain)	11.3		5.8		0.1		(0.1)
Net cost (benefit)	7.9		6.9		(0.2)		(0.4)
Change in associated regulatory liabilities	—		—		(1.0)		(1.0)
Net cost (benefit) after change in regulatory liabilities	$	7.9	$	6.9	$	(1.2)	$	(1.4)