Goodwill and Purchased Intangible Assets (Details 3) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Mar. 31, 2017	Sep. 30, 2016
Purchased intangible assets
Weighted- Average Life (in years)	14 years 9 months	14 years 6 months
Gross	$ 723.1	$ 727.4
Accumulated Amortization	(581.1)	(561.6)
Net	142.0	165.8
Non-amortizable trade names	387.7	387.7
Intangible assets excluding goodwill, gross	1,110.8	1,115.1
Purchased intangible assets, net	529.7	$ 553.5
Future amortization expense of purchased intangible assets for the five years succeeding fiscal year 2017
2017 (remaining six months)	22.2
2018	38.3
2019	36.9
2020	11.0
2021	5.3
2022	$ 4.9
Distribution network
Purchased intangible assets
Weighted- Average Life (in years)	39 years 1 month	39 years 1 month
Gross	$ 55.4	$ 55.4
Accumulated Amortization	(28.7)	(28.0)
Net	$ 26.7	$ 27.4
Technology-related
Purchased intangible assets
Weighted- Average Life (in years)	11 years 11 months	11 years 11 months
Gross	$ 104.7	$ 104.7
Accumulated Amortization	(95.7)	(91.5)
Net	$ 9.0	$ 13.2
Customer relationships
Purchased intangible assets
Weighted- Average Life (in years)	12 years 10 months	12 years 10 months
Gross	$ 546.6	$ 550.8
Accumulated Amortization	(442.0)	(427.4)
Net	$ 104.6	$ 123.4
Other
Purchased intangible assets
Weighted- Average Life (in years)	16 years 2 months	16 years 4 months
Gross	$ 16.4	$ 16.5
Accumulated Amortization	(14.7)	(14.7)
Net	$ 1.7	$ 1.8