Retirement Benefits - Narrative (Details) - USD ($)	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Defined Benefit Plan Disclosure [Line Items]
Expense related to defined contribution savings plans	$ 50,900,000	$ 53,100,000	$ 47,000,000.0
Defined benefit plan, percentage of benefit obligation relating to domestic plan	76.00%
Recognized prior service credits	$ (4,500,000)
Recognized prior service credits, net of tax	(3,500,000)
Recognized net actuarial losses	148,700,000
Recognized net actuarial losses, net of tax	113,000,000.0
Accumulated benefit obligation for pension plans	4,638,100,000	4,548,800,000
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Voluntary contribution to U.S. qualified pension plan	84,100,000	30,900,000
Recognized prior service credits	900,000	1,200,000	600,000
Recognized net actuarial losses	147,300,000	77,800,000	113,400,000
Estimated future payments, during next fiscal year	83,800,000
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Voluntary contribution to U.S. qualified pension plan	4,800,000	9,400,000
Recognized prior service credits	(5,400,000)	(5,400,000)	(5,500,000)
Recognized net actuarial losses	1,400,000	$ 900,000	$ 1,700,000
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	2.90%	3.30%	4.35%
U.S. Plans | Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Discount rate	2.15%	2.90%
Non-U.S. Plans | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Discount rate	1.56%	1.60%
Non-U.S. Plans | Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Discount rate	2.20%	2.65%
Qualified Plan | U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Voluntary contribution to U.S. qualified pension plan	$ 50,000,000.0	$ 0	$ 0