Goodwill and Acquired Intangible Assets (Narrative) (Details) $ in Millions	3 Months Ended	6 Months Ended	12 Months Ended
	Sep. 30, 2016 USD ($) segments	Apr. 02, 2016 segments	Sep. 30, 2016 USD ($) segments	Sep. 30, 2015 USD ($)
Number of reportable segments | segments	3	2	3
Estimated aggregate future amortization expense for intangible assets, 2016	$ 58.0		$ 58.0
Estimated aggregate future amortization expense for intangible assets, 2017	57.0		57.0
Estimated aggregate future amortization expense for intangible assets, 2018	49.9		49.9
Estimated aggregate future amortization expense for intangible assets, 2019	47.2		47.2
Estimated aggregate future amortization expense for intangible assets, 2020	41.8		41.8
Estimated aggregate future amortization expense for intangible assets, thereafter	56.5		56.5
Solutions Group [Member]
Goodwill and acquired intangible assets	1,196.6		1,196.6
Technology Platform Group [Member]
Goodwill and acquired intangible assets	252.8		252.8
Professional Services [Member]
Goodwill and acquired intangible assets	$ 30.7		$ 30.7
Software Products [Member]
Goodwill and acquired intangible assets				$ 1,297.9
Services [Member]
Goodwill and acquired intangible assets				$ 62.4