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		6 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2014	Mar. 31, 2013
Finite-Lived Intangible Assets [Line Items]
Amortization of intangibles	$ 37.4	$ 49.0	$ 80.8	$ 135.6
Customer relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Amortization of intangibles	11.6	11.3	23.3	21.7
Trade names [Member]
Finite-Lived Intangible Assets [Line Items]
Amortization of intangibles	4.1	4.3	8.2	7.9
Technology assets [Member]
Finite-Lived Intangible Assets [Line Items]
Amortization of intangibles	4.8	4.5	9.2	7.6
Definite Lived Intangible Assets [Member]
Finite-Lived Intangible Assets [Line Items]
Amortization of intangibles	$ 20.5	$ 20.1	$ 40.7	$ 37.2