Goodwill and Intangibles - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	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	$ 23.6	$ 20.5
Finite-Lived Intangible Assets, Accumulated Amortization	421.3		$ 399.2
VOBA [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months	93.9
2014	93.0
2015	86.2
2016	85.1
2017	84.9
Trade Names [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Accumulated Amortization	$ 77.5		$ 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