Retirement Benefits (Details 1) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Plan assets at beginning of year	$ 3,447.9
Company contributions	200.0
Plan assets at end of year	3,788.3	$ 3,447.9
Net amount on balance sheet consists of:
Retirement benefits	(892.5)	(1,430.2)
Pension Benefits [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of year	4,785.9	4,282.2
Service cost	97.0	88.0	$ 85.7
Interest cost	151.6	169.5	167.2
Actuarial losses (gains)	(221.9)	515.4
Plan amendments	(6.9)	(10.0)
Plan participant contributions	3.9	4.3
Benefits paid	(251.9)	(232.0)
Special termination benefit	0.5	0.5	0.0
Settlements	(13.8)	0.0
Curtailments	(1.0)	0.0
Currency translation and other	41.6	(32.0)
Benefit obligation at end of year	4,585.0	4,785.9	4,282.2
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Plan assets at beginning of year	3,447.9	3,262.5
Actual return on plan assets	315.5	394.3
Company contributions	254.9	44.3
Plan participant contributions	3.9	4.3
Benefits paid	(251.9)	(232.0)
Settlements	(2.8)	0.0	0.0
Currency translation and other	31.8	(25.5)
Plan assets at end of year	3,788.3	3,447.9	3,262.5
Funded status of plans	(796.7)	(1,338.0)
Net amount on balance sheet consists of:
Other assets	10.6	0.1
Compensation and benefits	(11.7)	(11.6)
Retirement benefits	(795.6)	(1,326.5)
Net amount on balance sheet	(796.7)	(1,338.0)
Other Postretirement Benefits [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of year	86.9	93.3
Service cost	1.4	1.3	1.5
Interest cost	2.5	3.3	4.1
Actuarial losses (gains)	(3.8)	(0.2)
Plan participant contributions	3.4	4.0
Benefits paid	(13.4)	(14.9)
Special termination benefit	0.0	0.0	0.0
Settlements	0.0	0.0
Curtailments	0.0	0.0
Currency translation and other	0.8	0.1
Benefit obligation at end of year	77.8	86.9	93.3
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Plan assets at beginning of year	0.0	0.0
Actual return on plan assets	0.0	0.0
Company contributions	10.0	10.9
Plan participant contributions	3.4	4.0
Benefits paid	(13.4)	(14.9)
Settlements	0.0	0.0	0.0
Currency translation and other	0.0	0.0
Plan assets at end of year	0.0	0.0	$ 0.0
Funded status of plans	(77.8)	(86.9)
Net amount on balance sheet consists of:
Other assets	0.0	0.0
Compensation and benefits	(9.5)	(10.5)
Retirement benefits	(68.3)	(76.4)
Net amount on balance sheet	$ (77.8)	$ (86.9)