Goodwill and Intangibles, including DAC and VOBA - Summary of Amortization Expense of Definite Lived Intangible Assets (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Finite-Lived Intangible Assets [Line Items]
Amortization of intangibles	$ 31.8	$ 43.4
Customer relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Amortization of intangibles	11.7	11.7
Trade names [Member]
Finite-Lived Intangible Assets [Line Items]
Amortization of intangibles	4.1	4.1
Technology assets [Member]
Finite-Lived Intangible Assets [Line Items]
Amortization of intangibles	4.7	4.4
Definite Lived Intangible Assets [Member]
Finite-Lived Intangible Assets [Line Items]
Amortization of intangibles	$ 20.5	$ 20.2