Employee Benefit Plans - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2025
Defined Benefit Plan Disclosure [Line Items]
Prior service cost included in accumulated other comprehensive loss	$ 2.3
Prior service cost included in accumulated other comprehensive loss, net of tax	1.7
Unrecognized net actuarial losses included in accumulated other comprehensive loss	4.9
Unrecognized net actuarial losses included in accumulated other comprehensive loss, net of tax	$ 3.7
Health care cost trend rate
Health care cost trend rate (as a percent)	6.50%
Increase in accumulated postretirement benefit obligation with 100 basis points increase in health care cost trend rate	$ 9.9
Increase in net periodic postretirement benefit cost with 100 basis points increase in health care cost trend rate	0.8
Decrease in accumulated postretirement benefit obligation with 100 basis points decrease in health care cost trend rate	7.5
Decrease in net periodic postretirement benefit cost with 100 basis points decrease in health care cost trend rate	0.6
Defined benefit plan, expected future employer contributions, next fiscal year	$ 25.0
Multi-Employer Pension Plans
Multiemployer plans, collective-bargaining arrangement, expiration date	May 01, 2022
Maximum Percent of Total Plan Contributions Contributed to Multi-employer Plan	5.00%	5.00%	5.00%
Multiemployer plan period contributions	$ 1.5	$ 1.4	$ 1.3
401(k) plans
Amounts expensed (income recognized) for matching and discretionary contributions	39.5	43.3	42.9
Scenario Forecast
Health care cost trend rate
Health care cost trend rate (as a percent)				5.00%
Supplemental Executive Retirement Plans
Defined Benefit Plan Disclosure [Line Items]
Trust held assets	21.4
Defined contribution SERP expense	$ 1.6	$ 1.6	$ 2.0
Minimum
401(k) plans
Percentage contribution by employees for defined contribution 401(k) plans, low end of range (as a percent)	2.00%
Employer contribution	2.00%
Maximum
401(k) plans
Percentage contribution by employees for defined contribution 401(k) plans, low end of range (as a percent)	100.00%
Employer contribution	6.00%