Derivative Financial Instruments - Summary of Gain (Loss) Recognized in Income on Derivatives (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Derivative Instruments, Gain (Loss) [Line Items]
Embedded Derivative, Gain (Loss) on Embedded Derivative, Net	$ 0.6
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]
Three months ended December 31,	0	(47.2)
Commodity contracts [Member] | Other (expense) income, net [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Three months ended December 31,	18.7	(3.4)
Bronze Commodity Contract [Member] | Consumer products cost of goods sold [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Three months ended December 31,	0	(0.1)
Bronze Commodity Contract [Member] | Net investment gains [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Three months ended December 31,	0.6	0
Foreign Exchange Contract [Member] | Other (expense) income, net [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Three months ended December 31,	(1.7)	0.8
Call options [Member] | Net investment gains [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Three months ended December 31,	41.3	114.3
Futures contracts [Member] | Net investment gains [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Three months ended December 31,	4.2	13.1
FIA embedded derivatives [Member] | Benefits and other changes in policy reserves [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Three months ended December 31,	$ 232.1	$ 100.3