Derivative Financial Instruments - Fair Value of Outstanding Derivative Contracts in Condensed Consolidated Balance Sheets (Detail) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Mar. 31, 2014	Sep. 30, 2013
Derivatives, Fair Value [Line Items]
Document Period End Date	Mar. 31, 2014
Total asset derivatives	$ 273.0	$ 221.8
Derivatives	273.0	221.8
Call options [Member]
Derivatives, Fair Value [Line Items]
Total asset derivatives	271.5	221.8
Derivatives designated as hedging instruments [Member]
Derivatives, Fair Value [Line Items]
Total asset derivatives	2.4	2.1
Total liability derivatives	5.2	5.2
Derivatives designated as hedging instruments [Member] | Commodity swap and option agreements [Member] | Receivables, net [Member]
Derivatives, Fair Value [Line Items]
Total asset derivatives	0.3	0.4
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	0
Derivatives designated as hedging instruments [Member] | Foreign exchange forward agreements [Member] | Receivables, net [Member]
Derivatives, Fair Value [Line Items]
Total asset derivatives	2.0	1.7
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	4.8	4.6
Derivatives designated as hedging instruments [Member] | Foreign exchange contracts [Member] | Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Total liability derivatives	0.2	0.1
Derivatives designated as hedging instruments [Member] | Commodity contracts [Member] | Accounts payable and other current liabilities [Member]
Derivatives, Fair Value [Line Items]
Total liability derivatives	0.2	0.5
Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Total asset derivatives	276.7	227.7
Total liability derivatives	2,095.8	1,888.6
Not Designated as Hedging Instrument [Member] | Equity conversion feature of preferred stock [Member]
Derivatives, Fair Value [Line Items]
Total liability derivatives	364.8	330.8
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		5.3
Not Designated as Hedging Instrument [Member] | Foreign exchange forward agreements [Member] | Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Total liability derivatives	2.2
Not Designated as Hedging Instrument [Member] | Foreign exchange contracts [Member] | Receivables, net [Member]
Derivatives, Fair Value [Line Items]
Total asset derivatives	0.1	0.1
Not Designated as Hedging Instrument [Member] | Commodity contracts [Member] | Receivables, net [Member]
Derivatives, Fair Value [Line Items]
Total asset derivatives		3.7
Not Designated as Hedging Instrument [Member] | Commodity contracts [Member] | Derivatives For Trading And Investment [Member]
Derivatives, Fair Value [Line Items]
Total asset derivatives	0
Not Designated as Hedging Instrument [Member] | Commodity contracts [Member] | Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Total liability derivatives	4.9	1.9
Not Designated as Hedging Instrument [Member] | Call options [Member] | Derivatives For Trading And Investment [Member]
Derivatives, Fair Value [Line Items]
Total asset derivatives	271.5	221.8
Not Designated as Hedging Instrument [Member] | FIA embedded derivatives [Member] | Contractholder funds [Member]
Derivatives, Fair Value [Line Items]
Total liability derivatives	1,718.7	1,544.4
Not Designated as Hedging Instrument [Member] | Futures contracts [Member] | Derivatives For Trading And Investment [Member]
Derivatives, Fair Value [Line Items]
Total asset derivatives	1.5	0
Not Designated as Hedging Instrument [Member] | Futures contracts [Member] | Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Total liability derivatives	0	1.0
Not Designated as Hedging Instrument [Member] | FX embedded derivative included in asset-based loans [Member] | Receivables, net [Member]
Derivatives, Fair Value [Line Items]
Total asset derivatives		$ 0