Derivative Financial Instruments - Fair Value of Outstanding Derivative Contracts in Condensed Consolidated Balance Sheets (Detail) - USD ($) $ in Millions	Sep. 30, 2015	Sep. 30, 2014
Call options
Derivatives, Fair Value [Line Items]
Total asset derivatives	$ 80.7	$ 296.3
Derivatives designated as hedging instruments
Derivatives, Fair Value [Line Items]
Total asset derivatives	5.6	14.2
Total liability derivatives	9.6	1.9
Derivatives designated as hedging instruments \| Interest Rate Swap [Member] \| Other assets
Derivatives, Fair Value [Line Items]
Total asset derivatives	0.0	0.6
Derivatives designated as hedging instruments \| Interest Rate Contract [Member] \| Accounts payable and other current liabilities
Derivatives, Fair Value [Line Items]
Total liability derivatives	1.4	1.8
Derivatives designated as hedging instruments \| Interest Rate Contract [Member] \| Other liabilities
Derivatives, Fair Value [Line Items]
Total liability derivatives	1.2	0.0
Derivatives designated as hedging instruments \| Commodity swap and option agreements \| Receivables, net
Derivatives, Fair Value [Line Items]
Total asset derivatives	0.0	1.3
Derivatives designated as hedging instruments \| Foreign exchange forward agreements \| Other assets
Derivatives, Fair Value [Line Items]
Total asset derivatives	0.4	0.3
Derivatives designated as hedging instruments \| Foreign exchange contracts \| Receivables, net
Derivatives, Fair Value [Line Items]
Total asset derivatives	5.2	12.0
Derivatives designated as hedging instruments \| Foreign exchange contracts \| Accounts payable and other current liabilities
Derivatives, Fair Value [Line Items]
Total liability derivatives	1.5	0.0
Derivatives designated as hedging instruments \| Commodity contracts \| Accounts payable and other current liabilities
Derivatives, Fair Value [Line Items]
Total liability derivatives	4.7	0.1
Derivatives designated as hedging instruments \| Commodity contracts \| Other liabilities
Derivatives, Fair Value [Line Items]
Total liability derivatives	0.8	0.0
Derivatives not designated as hedging instrument
Derivatives, Fair Value [Line Items]
Total asset derivatives	106.0	324.1
Total liability derivatives	2,159.2	1,910.9
Derivatives not designated as hedging instrument \| Foreign exchange forward agreements \| Accounts payable and other current liabilities
Derivatives, Fair Value [Line Items]
Total liability derivatives	0.1	0.1
Derivatives not designated as hedging instrument \| Foreign exchange contracts \| Receivables, net
Derivatives, Fair Value [Line Items]
Total asset derivatives	0.4	0.5
Derivatives not designated as hedging instrument \| Commodity contracts \| Receivables, net
Derivatives, Fair Value [Line Items]
Total asset derivatives	7.9	1.9
Derivatives not designated as hedging instrument \| Commodity contracts \| Accounts payable and other current liabilities
Derivatives, Fair Value [Line Items]
Total liability derivatives	0.1	0.0
Derivatives not designated as hedging instrument \| Commodity contracts \| Other liabilities
Derivatives, Fair Value [Line Items]
Total liability derivatives	0.0	0.3
Derivatives not designated as hedging instrument \| Call options \| Derivatives
Derivatives, Fair Value [Line Items]
Total asset derivatives	80.7	296.3
Derivatives not designated as hedging instrument \| Future contracts \| Derivatives
Derivatives, Fair Value [Line Items]
Total asset derivatives	1.2	0.0
Derivatives not designated as hedging instrument \| FIA embedded derivatives \| Contractholder funds
Derivatives, Fair Value [Line Items]
Total liability derivatives	2,149.4	1,908.1
Derivatives not designated as hedging instrument \| Futures contracts \| Other liabilities
Derivatives, Fair Value [Line Items]
Total liability derivatives	0.0	0.5
Derivatives not designated as hedging instrument \| Futures contracts \| Derivatives
Derivatives, Fair Value [Line Items]
Total asset derivatives	$ 10.2	$ 11.2