Retirement Benefits (Assumptions in Calculating Net Periodic Benefit Cost) (Details)		12 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
U.S.
Defined Benefit Plan Disclosure [Line Items]
Expected return on plan assets		8.00%
International
Defined Benefit Plan Disclosure [Line Items]
Expected return on plan assets		6.10%
Defined Benefit Pension Plan | U.S.
Defined Benefit Plan Disclosure [Line Items]
Discount rate	[1]	3.50%	4.30%	4.30%
Expected return on plan assets		8.00%	8.00%	8.30%
Rate of compensation increase		3.50%	3.50%	3.50%
Discount rate used to measure service cost		3.60%
Discount rate used to measure interest cost		3.00%
Defined Benefit Pension Plan | International
Defined Benefit Plan Disclosure [Line Items]
Discount rate	[1]	2.00%	3.30%	3.60%
Expected return on plan assets		6.10%	6.30%	6.10%
Rate of compensation increase		3.50%	3.50%	3.60%
Discount rate used to measure service cost		2.10%
Discount rate used to measure interest cost		1.80%

[1] Effective in 2016, the Company began to measure the service cost and interest cost components of pension expense by applying spot rates along the yield curve to the relevant projected cash flows, as we believe this provides a better measurement of these costs. The Company accounted for this in 2016 as a change in accounting estimate and, accordingly, accounted for it on a prospective basis. This change did not affect the measurement of the total benefit obligation. The 2017 discount rates used to measure the service cost and interest cost of our U.S. pension plans were 3.6% and 3.0%, respectively. The rates used to measure the service cost and interest cost of our major International pension plans were 2.1% and 1.8%, respectively. The previous method would have used a single discount rate for both service and interest costs.