Goodwill and Intangibles - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Sep. 30, 2015
Finite-Lived Intangible Assets [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent			35.00%
Amortization of intangibles	$ 23.5	$ 22.3	$ 70.5	$ 64.0
Finite-Lived Intangible Assets, Accumulated Amortization	465.0		465.0		$ 399.2
Finite-Lived Intangible Assets [Member]
Finite-Lived Intangible Assets [Line Items]
Amortization of intangibles	23.5	$ 22.3	70.5	$ 64.0
VOBA [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months	93.9		93.9
2014	93.0		93.0
2015	86.2		86.2
2016	85.1		85.1
2017	84.9		84.9
Trade Names [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Accumulated Amortization	$ 85.3		$ 85.3		$ 73.7
Minimum [Member] | Technology Assets [Member]
Finite-Lived Intangible Assets [Line Items]
Amortizable Life			4 years
Minimum [Member] | Trade Names [Member]
Finite-Lived Intangible Assets [Line Items]
Amortizable Life			8 years
Maximum [Member] | Technology Assets [Member]
Finite-Lived Intangible Assets [Line Items]
Amortizable Life			18 years
Maximum [Member] | Trade Names [Member]
Finite-Lived Intangible Assets [Line Items]
Amortizable Life			17 years
Weighted Average [Member] | Technology Assets [Member]
Finite-Lived Intangible Assets [Line Items]
Amortizable Life			11 years 1 month 6 days
Weighted Average [Member] | Trade Names [Member]
Finite-Lived Intangible Assets [Line Items]
Amortizable Life			16 years 2 months 12 days