Employee Benefit Plans - Schedule of Change in Benefit Obligations (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Change in benefit obligations
Benefit obligations at beginning of period	$ 1,500.0
Actuarial loss (gain)	(2.4)	$ (41.6)	$ 43.9
Benefit obligations at end of period	1,600.0	1,500.0
Amounts in the Consolidated Balance Sheets
Noncurrent benefit liabilities (c)	176.2	168.0
Pension benefits
Change in benefit obligations
Benefit obligations at beginning of period	1,478.1	1,585.2
Interest cost	83.4	81.8	43.0
Benefits paid	(130.6)	(130.4)
Actuarial loss (gain)	140.0	(52.7)
Transfers in	1.6	4.4
Settlements	(6.8)	(10.2)
Benefit obligations at end of period	1,565.7	1,478.1	1,585.2
Change in plan assets
Fair value of plan assets at beginning of period	1,361.0	1,438.1
Actual return on plan assets	213.5	41.3
Employer contributions	14.2	17.8
Benefits paid	(130.6)	(130.4)
Settlements	(6.8)	(10.2)
Transfers in	1.6	4.4
Fair value of plan assets at end of period	1,452.9	1,361.0	1,438.1
Unfunded status of the plans as of September 30	112.8	117.1
Amounts in the Consolidated Balance Sheets
Noncurrent benefit assets (a)	49.0	38.6
Current benefit liabilities (b)	7.1	7.7
Noncurrent benefit liabilities (c)	154.7	148.0
Total benefit liabilities	161.8	155.7
Net liabilities recognized	112.8	117.1
Balance in Accumulated other comprehensive loss
Prior service cost (credit)	$ 1.1	$ 1.1
Weighted-average plan assumptions
Discount rate	4.94%	5.98%
Other postretirement benefits
Change in benefit obligations
Benefit obligations at beginning of period	$ 22.3	$ 30.7
Interest cost	1.2	1.2	0.7
Benefits paid	(2.4)	(3.0)
Actuarial loss (gain)	2.7	(6.6)
Transfers in	0.0	0.0
Settlements	0.0	0.0
Benefit obligations at end of period	23.8	22.3	30.7
Change in plan assets
Fair value of plan assets at beginning of period	0.0	0.0
Actual return on plan assets	0.0	0.0
Employer contributions	2.4	3.0
Benefits paid	(2.4)	(3.0)
Settlements	0.0	0.0
Transfers in	0.0	0.0
Fair value of plan assets at end of period	0.0	0.0	$ 0.0
Unfunded status of the plans as of September 30	23.8	22.3
Amounts in the Consolidated Balance Sheets
Noncurrent benefit assets (a)	0.0	0.0
Current benefit liabilities (b)	2.7	2.6
Noncurrent benefit liabilities (c)	21.1	19.7
Total benefit liabilities	23.8	22.3
Net liabilities recognized	23.8	22.3
Balance in Accumulated other comprehensive loss
Prior service cost (credit)	$ (14.4)	$ (16.7)
Weighted-average plan assumptions
Discount rate	4.89%	5.98%
Assumed pre-65 health care cost trend rate	7.20%	5.50%
Ultimate pre-65 health care cost trend rate	4.00%