Employee Benefit Plans - Schedule of Change in Benefit Obligations (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
Change in benefit obligations
Benefit obligations at beginning of period	$ 2,100.0
Actuarial (gain) loss	43.9	$ (74.3)	$ (18.6)
Benefit obligations at end of period	1,600.0	2,100.0
Amounts in the Consolidated Balance Sheets
Noncurrent benefit liabilities (c)	199.4	245.1
Pension benefits
Change in benefit obligations
Benefit obligations at beginning of period	2,132.9	2,251.7
Interest cost	43.0	41.2	59.6
Benefits paid	(128.0)	(130.3)
Actuarial (gain) loss	(458.3)	(31.7)
Transfers in	0.5	3.2
Settlements	(4.9)	(1.2)
Benefit obligations at end of period	1,585.2	2,132.9	2,251.7
Change in plan assets
Fair value of plan assets at beginning of period	1,987.0	1,977.9
Actual return on plan assets	(429.5)	127.7
Employer contributions	13.0	9.7
Benefits paid	(128.0)	(130.3)
Settlements	(4.9)	(1.2)
Transfers in	0.5	3.2
Fair value of plan assets at end of period	1,438.1	1,987.0	1,977.9
Unfunded status of the plans as of September 30	147.1	145.9
Assets for Plan Benefits, Defined Benefit Plan	33.7	71.5
Amounts in the Consolidated Balance Sheets
Current benefit liabilities (b)	9.1	9.3
Noncurrent benefit liabilities (c)	171.7	208.1
Net liabilities recognized	180.8	217.4
Balance in Accumulated other comprehensive loss
Prior service cost (credit)	$ 1.2	$ 1.3
Weighted-average plan assumptions
Discount rate	5.58%	2.70%
Pension benefits | Liability
Amounts in the Consolidated Balance Sheets
Net liabilities recognized	$ 147.1	$ 145.9
Other postretirement benefits
Change in benefit obligations
Benefit obligations at beginning of period	38.9	41.6
Interest cost	0.7	0.7	1.1
Benefits paid	(3.3)	(4.1)
Actuarial (gain) loss	(5.6)	0.7
Transfers in	0.0	0.0
Settlements	0.0	0.0
Benefit obligations at end of period	30.7	38.9	41.6
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	3.3	4.1
Benefits paid	(3.3)	(4.1)
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	30.7	38.9
Assets for Plan Benefits, Defined Benefit Plan	0.0	0.0
Amounts in the Consolidated Balance Sheets
Current benefit liabilities (b)	4.4	4.2
Noncurrent benefit liabilities (c)	26.3	34.7
Net liabilities recognized	30.7	38.9
Balance in Accumulated other comprehensive loss
Prior service cost (credit)	$ (18.9)	$ (21.1)
Weighted-average plan assumptions
Discount rate	5.56%	2.53%
Assumed pre-65 health care cost trend rate	5.60%	5.70%
Ultimate pre-65 health care cost trend rate	4.00%