Retirement Benefits - Narrative (Details) - USD ($)	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Defined Benefit Plan Disclosure [Line Items]
Expense related to defined contribution savings plans	$ 53,100,000	$ 47,000,000.0	$ 41,500,000
Recognized prior service credits	(4,200,000)
Recognized prior service credits, net of tax	(3,200,000)
Recognized net actuarial losses	78,700,000
Recognized net actuarial losses, net of tax	59,700,000
Accumulated benefit obligation for pension plans	$ 4,548,800,000	3,962,300,000
Defined benefit plan, percentage of benefit obligation relating to domestic plan	76.00%
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Voluntary contribution to U.S. qualified pension plan	$ 30,900,000	50,300,000
Recognized prior service credits	1,200,000	600,000	(3,700,000)
Recognized net actuarial losses	77,800,000	113,400,000	152,900,000
Estimated future payments, during next fiscal year	32,200,000
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Voluntary contribution to U.S. qualified pension plan	9,400,000	10,100,000
Recognized prior service credits	(5,400,000)	(5,500,000)	(6,100,000)
Recognized net actuarial losses	900,000	$ 1,700,000	$ 2,300,000
Estimated future payments, during next fiscal year	$ 7,400,000
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	3.30%	4.35%	3.90%
U.S. Plans | Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Discount rate	2.90%	4.15%
Non-U.S. Plans | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Discount rate	1.60%	2.48%
Non-U.S. Plans | Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Discount rate	2.65%	3.30%
Qualified Plan | U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Voluntary contribution to U.S. qualified pension plan	$ 0	$ 0	$ 200,000,000.0