Derivative Financial Instruments - Fair Value of Outstanding Derivative Contracts in Condensed Consolidated Balance Sheets (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Sep. 30, 2012
Derivatives, Fair Value [Line Items]
Total asset derivatives	$ 262.6	$ 200.7
Call options [Member]
Derivatives, Fair Value [Line Items]
Total asset derivatives	262.0	200.7
Derivatives designated as hedging instruments [Member]
Derivatives, Fair Value [Line Items]
Total asset derivatives	3.3	3.2
Total liability derivatives	1.6	3.1
Derivatives designated as hedging instruments [Member] | Commodity swap and option agreements [Member] | Receivables, net [Member]
Derivatives, Fair Value [Line Items]
Total asset derivatives	0.1	1.0
Derivatives designated as hedging instruments [Member] | Commodity swap and option agreements [Member] | Other assets [Member]
Derivatives, Fair Value [Line Items]
Total asset derivatives	0.1	1.0
Derivatives designated as hedging instruments [Member] | Foreign exchange forward agreements [Member] | Receivables, net [Member]
Derivatives, Fair Value [Line Items]
Total asset derivatives	3.0	1.2
Derivatives designated as hedging instruments [Member] | Foreign exchange forward agreements [Member] | Accounts payable and other current liabilities [Member]
Derivatives, Fair Value [Line Items]
Total liability derivatives	0.7	3.1
Derivatives designated as hedging instruments [Member] | Foreign exchange contracts [Member] | Other assets [Member]
Derivatives, Fair Value [Line Items]
Total asset derivatives	0.1	0
Derivatives designated as hedging instruments [Member] | Foreign exchange contracts [Member] | Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Total liability derivatives	0.1	0
Derivatives designated as hedging instruments [Member] | Commodity contracts [Member] | Accounts payable and other current liabilities [Member]
Derivatives, Fair Value [Line Items]
Total liability derivatives	0.7	0
Derivatives designated as hedging instruments [Member] | Commodity contracts [Member] | Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Total liability derivatives	0.1	0
Derivatives Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Total asset derivatives	266.0	203.9
Total liability derivatives	1,856.2	1,793.7
Derivatives Not Designated as Hedging Instrument [Member] | Equity conversion feature of preferred stock [Member]
Derivatives, Fair Value [Line Items]
Total liability derivatives	202.7	232.0
Derivatives Not Designated as Hedging Instrument [Member] | Foreign exchange forward agreements [Member] | Accounts payable and other current liabilities [Member]
Derivatives, Fair Value [Line Items]
Total liability derivatives	3.2	4.0
Derivatives Not Designated as Hedging Instrument [Member] | Foreign exchange forward agreements [Member] | Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Total liability derivatives	0.8	2.9
Derivatives Not Designated as Hedging Instrument [Member] | Foreign exchange contracts [Member] | Receivables, net [Member]
Derivatives, Fair Value [Line Items]
Total asset derivatives	0.1	0
Derivatives Not Designated as Hedging Instrument [Member] | Commodity contracts [Member] | Derivatives [Member]
Derivatives, Fair Value [Line Items]
Total asset derivatives	0.2	0
Derivatives Not Designated as Hedging Instrument [Member] | Commodity contracts [Member] | Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Total liability derivatives	8.3	0
Derivatives Not Designated as Hedging Instrument [Member] | Call options [Member] | Derivatives [Member]
Derivatives, Fair Value [Line Items]
Total asset derivatives	262.0	200.7
Derivatives Not Designated as Hedging Instrument [Member] | FIA embedded derivatives [Member] | Contractholder funds [Member]
Derivatives, Fair Value [Line Items]
Total liability derivatives	1,639.6	1,550.8
Derivatives Not Designated as Hedging Instrument [Member] | Futures contracts [Member] | Derivatives [Member]
Derivatives, Fair Value [Line Items]
Total asset derivatives	0.4	0
Derivatives Not Designated as Hedging Instrument [Member] | Futures contracts [Member] | Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Total liability derivatives		$ 0.9