Derivative Financial Instruments - Summary of Gain (Loss) Recognized in Income on Derivatives (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
Derivative Instruments, Gain (Loss) [Line Items]
Document Period End Date			Mar. 31, 2014
Gain (Loss) Recognized in Income on Derivatives	$ 87.2	$ (37.0)	$ 265.0	$ 36.0
Equity conversion feature of preferred stock [Member] | Gain from the change in the fair value of the equity conversion feature of preferred stock [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on Derivatives	(3.5)	(39.6)	(50.7)	29.3
Commodity contracts [Member] | Other (expense) income, net [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on Derivatives	(6.8)	(8.8)	(10.2)	(8.8)
Bronze Commodity Contract [Member] | Other (expense) income, net [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on Derivatives		0
Bronze Commodity Contract [Member] | Consumer products cost of goods sold [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on Derivatives	0		(0.1)	0
Foreign exchange contracts [Member] | Other (expense) income, net [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on Derivatives	(0.2)	1.8	0.6	(2.3)
FX embedded derivative included in asset-based loans [Member] | Other (expense) income, net [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on Derivatives	1.2	0	1.2	0
Call options [Member] | Net investment gains [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on Derivatives	21.2	118.5	135.5	97.6
Futures contracts [Member] | Net investment gains [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on Derivatives	1.3	13.7	14.4	9.0
FIA embedded derivatives [Member] | Benefits and other changes in policy reserves [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on Derivatives	$ 74.0	$ (122.6)	$ 174.3	$ (88.8)