Retirement Plans - Summary of Components of Net Pension Income and Summary of Components of Postretirement Benefit Cost (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 10.7	$ 11.2	$ 35.9	$ 38.3
Interest cost	46.9	47.3	141.6	140.4
Expected return on plan assets	(92.0)	(92.0)	(277.0)	(276.0)
Amortization of net actuarial loss (gain)	2.3	9.8	6.7	25.7
Amortization of prior service cost (credit)	2.1	2.3	6.3	6.3
Settlement loss			0.2
Company defined benefit plan income	(30.0)	(21.4)	(86.3)	(65.3)
Multiemployer and other plans	0.4	0.4	1.1	1.2
Net pension (income) cost	(29.6)	(21.0)	(85.2)	(64.1)
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.3	0.2	0.8	0.8
Interest cost	1.7	1.5	4.8	4.4
Amortization of net actuarial loss (gain)	0.4	0.2	(0.4)	(0.4)
Amortization of prior service cost (credit)	(0.1)	(0.6)	(0.5)	(1.8)
Net pension (income) cost	$ 2.3	$ 1.3	$ 4.7	$ 3.0