Business Segment and Geographic Information (Reconciliation of Assets) (Details) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Segment Reporting Information [Line Items]
Total assets	$ 18,467.2	$ 18,028.6	$ 17,316.6
Segment Total
Segment Reporting Information [Line Items]
Total assets	18,457.0	16,060.1	14,760.0
Discontinued Operations | Segment Reconciling Items
Segment Reporting Information [Line Items]
Assets of discontinued operations	$ 10.2	$ 1,968.5	$ 2,556.6