Derivative Financial Instruments - Summary of Gain (Loss) Recognized in Income on Derivatives (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
Derivative Instruments, Gain (Loss) [Line Items]
Embedded Derivative, Gain (Loss) on Embedded Derivative, Net	$ (0.1)	$ 0	$ 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 Recognized in Income on Derivatives	(12.7)	(101.6)	(156.6)
Commodity contracts | Other (expense) income, net
Derivative Instruments, Gain (Loss) [Line Items]
Gain Recognized in Income on Derivatives	(6.6)	(1.3)	0
Bronze Commodity Contract | Consumer products cost of goods sold
Derivative Instruments, Gain (Loss) [Line Items]
Gain Recognized in Income on Derivatives	(0.1)	(0.1)	0
Foreign exchange contracts | Other (expense) income, net
Derivative Instruments, Gain (Loss) [Line Items]
Gain Recognized in Income on Derivatives	3.1	(3.6)	5.9
Call options | Net investment gains
Derivative Instruments, Gain (Loss) [Line Items]
Gain Recognized in Income on Derivatives	(246.0)	(151.6)	(100.0)
Futures contracts | Net investment gains
Derivative Instruments, Gain (Loss) [Line Items]
Gain Recognized in Income on Derivatives	(25.5)	(17.5)	(46.0)
Available-for-sale embedded derivatives | Net Investment Income
Derivative Instruments, Gain (Loss) [Line Items]
Gain Recognized in Income on Derivatives	0	0	(0.4)
FIA embedded derivatives | Benefits and other changes in policy reserves
Derivative Instruments, Gain (Loss) [Line Items]
Gain Recognized in Income on Derivatives	$ 363.7	$ (6.4)	$ 154.5