Derivative Financial Instruments - Summary of Gain (Loss) Recognized in Income on Derivatives (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on Derivatives	$ 56.1	$ 150.2	$ (218.0)
Equity conversion feature of preferred stock | Gain from the change in the fair value of the equity conversion feature of preferred stock
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on Derivatives	(101.6)	(156.6)	27.9
Commodity contracts | Other (expense) income, net
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on Derivatives	(1.3)	0	0
Bronze Commodity Contract | Consumer products cost of goods sold
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on Derivatives	(0.1)	0	0
Foreign exchange contracts | Other (expense) income, net
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on Derivatives	(3.6)	5.9	(5.1)
Call options | Net investment gains
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on Derivatives	151.6	100.0	(142.7)
Futures contracts | Net investment gains
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on Derivatives	17.5	46.0	(28.1)
Available-for-sale embedded derivatives | Net Investment Income
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on Derivatives	0	0.4	0
FIA embedded derivatives | Benefits and other changes in policy reserves
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on Derivatives	$ (6.4)	$ 154.5	$ (70.0)