Retirement Benefits (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2018		Sep. 30, 2017		Sep. 30, 2016
Defined Benefit Plan Disclosure [Line Items]
Pension settlement loss	$ 43.7	$ 48.5	[1]	$ 10.5	[1]	$ 5.1	[1]
Shares of common stock in ESOP	2,378,336	2,378,336
Defined contribution plan cost recognized		$ 34.2		33.7		34.6
Pension and postretirement benefits	$ 34.1	$ 34.1		22.6
U.S.
Defined Benefit Plan Disclosure [Line Items]
Expected return on plan assets		7.50%
U.S. | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Expected return on plan assets		8.00%
U.S. | Debt securities
Defined Benefit Plan Disclosure [Line Items]
Expected return on plan assets		5.40%
U.S. | Real estate/other
Defined Benefit Plan Disclosure [Line Items]
Expected return on plan assets		6.90%
International
Defined Benefit Plan Disclosure [Line Items]
Expected return on plan assets		5.80%
U.K.
Defined Benefit Plan Disclosure [Line Items]
Expected return on plan assets		6.20%
Percentage of plan assets as component of total international plan assets		80.00%
U.K. | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Expected return on plan assets		7.40%
U.K. | Debt securities
Defined Benefit Plan Disclosure [Line Items]
Expected return on plan assets		2.70%
Defined Benefit Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Pension settlement loss	43.7			10.5		5.1
ABO for all defined benefit pension plans	4,376.4	$ 4,376.4		4,842.8
Company contributions		68.3
Defined Benefit Pension Plan | Minimum
Defined Benefit Plan Disclosure [Line Items]
Anticipated contributions for next fiscal year	45.0	45.0
Defined Benefit Pension Plan | Maximum
Defined Benefit Plan Disclosure [Line Items]
Anticipated contributions for next fiscal year	65.0	65.0
Defined Benefit Pension Plan | Unfunded Plan
Defined Benefit Plan Disclosure [Line Items]
ABO for plans with obligation in excess plan assets	92.8	92.8
PBO for plans with obligation in excess of plan assets	100.9	100.9
Defined Benefit Pension Plan | U.S.
Defined Benefit Plan Disclosure [Line Items]
Pension settlement loss		$ 45.0		10.5		$ 5.1
Amortization period based on approximate average remaining service period		8 years
ABO for plans with obligation in excess plan assets	2,608.6	$ 2,608.6		2,951.0
PBO for plans with obligation in excess of plan assets	2,733.6	$ 2,733.6		$ 3,116.7
Expected return on plan assets		7.50%		8.00%		8.00%
Company contributions		$ 14.6		$ 27.2
Accumulated benefit obligations	2,922.8	2,922.8		3,357.7		$ 3,477.7
Pension and postretirement benefits	23.5	23.5		12.6
Gains arising during the period		(167.7)		(189.8)
Amortization of net actuarial loss		(132.4)		(103.3)
Net actuarial loss on pretax basis	680.4	680.4		980.5
Defined Benefit Pension Plan | International
Defined Benefit Plan Disclosure [Line Items]
Pension settlement loss		3.5		1.7		$ 1.3
ABO for plans with obligation in excess plan assets	357.9	357.9		365.6
PBO for plans with obligation in excess of plan assets	452.6	$ 452.6		$ 465.7
Expected return on plan assets		5.80%		6.10%		6.30%
Company contributions		$ 53.7		$ 42.2
Accumulated benefit obligations	1,660.5	1,660.5		1,749.5		$ 1,849.6
Pension and postretirement benefits	1.2	1.2		0.0
Gains arising during the period		(64.6)		(162.0)
Amortization of net actuarial loss		(43.7)		(55.7)
Net actuarial loss on pretax basis	443.6	$ 443.6		551.9
Defined Benefit Pension Plan | U.K.
Defined Benefit Plan Disclosure [Line Items]
Amortization period based on approximate average remaining life expectancy		26 years
Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligations	56.4	$ 56.4		67.0
Pension and postretirement benefits	9.4	9.4		10.0
Gains arising during the period		(3.1)		(10.7)
Amortization of net actuarial loss		(0.3)		(0.2)
Net actuarial loss on pretax basis	$ 4.4	$ 4.4		$ 7.8

[1] Fiscal year 2018 includes a loss of $43.7 that primarily resulted from the transfer of certain pension payment obligations to an insurer through the purchase of an irrevocable, nonparticipating group annuity contract during the fourth quarter.