Retirement Benefits - Narrative (Details) - USD ($)	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Defined Benefit Plan Disclosure [Line Items]
Expense related to defined contribution savings plans	$ 58,500,000	$ 50,900,000	$ 53,100,000
Defined benefit plan, percentage of benefit obligation relating to domestic plan	75.00%
Recognized prior service credits	$ 35,800,000
Recognized prior service credits, net of tax	29,900,000
Recognized net actuarial losses	142,500,000
Recognized net actuarial losses, net of tax	108,300,000
Accumulated benefit obligation for pension plans	4,393,000,000	4,638,100,000
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Voluntary contribution to U.S. qualified pension plan	34,900,000	84,100,000
Recognized prior service credits	1,400,000	900,000	1,200,000
Recognized net actuarial losses	141,400,000	147,300,000	77,800,000
Estimated future payments, during next fiscal year	57,400,000
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Voluntary contribution to U.S. qualified pension plan	5,700,000	4,800,000
Recognized prior service credits	(5,400,000)	(5,400,000)	(5,400,000)
Recognized net actuarial losses	1,100,000	$ 1,400,000	$ 900,000
Estimated future payments, during next fiscal year	$ 5,800,000
Minimum
Defined Benefit Plan Disclosure [Line Items]
Company contribution to defined contribution plan (percentage)	3.00%
Maximum
Defined Benefit Plan Disclosure [Line Items]
Company contribution to defined contribution plan (percentage)	7.00%
U.S. Plans | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.10%	2.90%	3.30%
U.S. Plans | Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Discount rate	2.50%	2.15%
Non-U.S. Plans | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Discount rate	2.03%	1.56%
Non-U.S. Plans | Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Discount rate	2.90%	2.20%
Qualified Plan | U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Voluntary contribution to U.S. qualified pension plan	$ 0	$ 50,000,000	$ 0