Defined Benefit Pension and Other Postretirement Plans - Narrative (Details) - USD ($)	3 Months Ended		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Defined Benefit Plans and Other Postretirement Benefit Plans
Contribution made to pension and post-retirement plans			$ 9,500,000	$ 8,200,000
Expected contribution to pension plan during remainder of fiscal year	$ 3,000,000.0		3,000,000.0
Defined benefit plan, net periodic benefit cost (credit)		$ 0	0	0
Nonqualified Plan | Defined Benefit Plan, Unfunded Plan
Defined Benefit Plans and Other Postretirement Benefit Plans
Defined benefit plan, net periodic benefit cost (credit)	0
Other Postretirement Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans
Contribution made to pension and post-retirement plans			0	0
Defined benefit plan, net periodic benefit cost (credit)	$ (100,000)	$ (100,000)	$ (200,000)	$ (400,000)