Fair Value of Financial Instruments - Schedule of Unobservable Inputs Used for Level Three Fair Value Measurements of Financial Instruments on Recurring Basis (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended												12 Months Ended																																											12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended				12 Months Ended					12 Months Ended			12 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013 Equity Securities	Sep. 30, 2014 Contingent purchase price reduction receivable	Sep. 30, 2013 Contingent purchase price reduction receivable	Sep. 30, 2014 FIA embedded derivatives, included in contractholder funds	Sep. 30, 2013 FIA embedded derivatives, included in contractholder funds	Sep. 30, 2014 FIA embedded derivatives, included in contractholder funds Fair Value, Measurements, Recurring	Sep. 30, 2013 FIA embedded derivatives, included in contractholder funds Fair Value, Measurements, Recurring	Sep. 30, 2014 Equity conversion feature of preferred stock	Sep. 30, 2013 Equity conversion feature of preferred stock	Sep. 30, 2014 Minimum Asset-backed securities	Sep. 30, 2013 Minimum Asset-backed securities	Sep. 30, 2014 Minimum Commercial mortgage-backed securities	Sep. 30, 2014 Minimum Corporates	Sep. 30, 2013 Minimum Corporates	Sep. 30, 2013 Minimum Hybrids	Sep. 30, 2014 Minimum Contingent purchase price reduction receivable	Sep. 30, 2013 Minimum Contingent purchase price reduction receivable	Sep. 30, 2014 Minimum FIA embedded derivatives, included in contractholder funds	Sep. 30, 2013 Minimum FIA embedded derivatives, included in contractholder funds	Sep. 30, 2014 Minimum Equity conversion feature of preferred stock	Sep. 30, 2013 Minimum Equity conversion feature of preferred stock	Sep. 30, 2014 Maximum Asset-backed securities	Sep. 30, 2013 Maximum Asset-backed securities	Sep. 30, 2014 Maximum Commercial mortgage-backed securities	Sep. 30, 2013 Maximum Commercial mortgage-backed securities	Sep. 30, 2014 Maximum Corporates	Sep. 30, 2013 Maximum Corporates	Sep. 30, 2013 Maximum Hybrids	Sep. 30, 2014 Maximum Contingent purchase price reduction receivable	Sep. 30, 2013 Maximum Contingent purchase price reduction receivable	Sep. 30, 2014 Maximum FIA embedded derivatives, included in contractholder funds	Sep. 30, 2013 Maximum FIA embedded derivatives, included in contractholder funds	Sep. 30, 2014 Maximum Equity conversion feature of preferred stock	Sep. 30, 2013 Maximum Equity conversion feature of preferred stock	Sep. 30, 2013 Weighted average	Sep. 30, 2014 Weighted average Asset-backed securities	Sep. 30, 2013 Weighted average Asset-backed securities	Sep. 30, 2014 Weighted average Commercial mortgage-backed securities	Sep. 30, 2014 Weighted average Corporates	Sep. 30, 2013 Weighted average Corporates	Sep. 30, 2014 Weighted average Equity Securities	Sep. 30, 2014 Weighted average Municipal Debt Securities [Member]	Sep. 30, 2013 Weighted average Hybrids	Sep. 30, 2014 Weighted average Contingent purchase price reduction receivable	Sep. 30, 2013 Weighted average Contingent purchase price reduction receivable	Sep. 30, 2014 Weighted average FIA embedded derivatives, included in contractholder funds	Sep. 30, 2013 Weighted average FIA embedded derivatives, included in contractholder funds	Sep. 30, 2014 Weighted average Equity conversion feature of preferred stock	Sep. 30, 2013 Weighted average Equity conversion feature of preferred stock	Sep. 30, 2014 Monte Carlo simulation / Option model Equity conversion feature of preferred stock	Sep. 30, 2014 Broker Quoted [Member] Asset-backed securities	Sep. 30, 2013 Broker Quoted [Member] Asset-backed securities	Sep. 30, 2014 Broker Quoted [Member] Commercial mortgage-backed securities	Sep. 30, 2013 Broker Quoted [Member] Commercial mortgage-backed securities	Sep. 30, 2014 Broker Quoted [Member] Corporates	Sep. 30, 2013 Broker Quoted [Member] Corporates	Sep. 30, 2014 Broker Quoted [Member] Municipal	Sep. 30, 2013 Broker Quoted [Member] Municipal	Sep. 30, 2014 Broker Quoted [Member] Equity Securities	Sep. 30, 2013 Broker Quoted [Member] Equity Securities	Sep. 30, 2014 Discounted Cash Flow [Member] Contingent purchase price reduction receivable	Sep. 30, 2014 Discounted Cash Flow [Member] FIA embedded derivatives, included in contractholder funds	Sep. 30, 2014 Matrix Pricing [Member] Corporates	Sep. 30, 2013 Matrix Pricing [Member] Corporates	Sep. 30, 2014 Option Pricing [Member] Equity Securities	Sep. 30, 2014 Option Pricing [Member] Other invested assets	Sep. 30, 2013 Option Pricing [Member] Other invested assets	Sep. 30, 2014 Fair Value, Inputs, Level 3 [Member] FIA embedded derivatives, included in contractholder funds Fair Value, Measurements, Recurring	Sep. 30, 2013 Fair Value, Inputs, Level 3 [Member] FIA embedded derivatives, included in contractholder funds Fair Value, Measurements, Recurring	Sep. 30, 2014 Fair Value, Inputs, Level 3 [Member] Front Street Future Policyholder Benefits Reserve [Member] Fair Value, Measurements, Recurring	Sep. 30, 2014 Other invested assets Fair Value, Measurements, Recurring	Sep. 30, 2014 Other invested assets Fair Value, Inputs, Level 3 [Member] Option Pricing [Member] Fair Value, Measurements, Recurring	Sep. 30, 2014 Front Street Future Policyholder Benefits Reserve [Member] Minimum	Sep. 30, 2014 Front Street Future Policyholder Benefits Reserve [Member] Maximum	Sep. 30, 2014 Front Street Future Policyholder Benefits Reserve [Member] Weighted average
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Document Period End Date	Sep. 30, 2014
Valuation Technique																																																					Monte Carlo simulation / Option model			Broker-quoted		Matrix pricing		Broker-quoted		Broker-quoted		Discounted cash flow	Discounted cash flow	Broker-quoted		Option Pricing	Black Scholes model				Discounted cash flow
Other invested assets	$ 165.0	$ 31.2																																																																								$ 13.3	$ 11.2
Assets, Fair Value Disclosure	1,066.0		523.5	10.7	41.5	41.0																																																37.0	5.0	83.1	5.7	848.0	404.5	37.2	0	6.0	0			2.0	56.6			0
Probability of collection																			88.00%	88.00%												96.00%	96.00%														92.00%	92.00%
Expected term																																4 months 15 days	9 months
Fair Value Inputs, Discount Rate																																1.00%	1.00%
Credit insurance risk premium																																12.00%	11.00%
Quoted prices																62.00%	0.00%													113.00%												100.00%	90.00%			0.00%
Offered quotes													100.00%		105.00%		90.00%								109.00%		121.00%	96.00%	120.00%	131.00%									101.00%	103.00%	118.00%	142.00%	97.00%	100.00%	107.00%	25.00%
Risk-free discount factor																																						0.999
Risk-adjusted discount factor																																						0.995
Upward movement factor (Mu)																																						1.1
Downward movement (Md)																																						0.9
Probability of upward movement (Pu)																																						48.60%
Probability of downward movement (Pd)																																						51.40%
Liabilities
Liabilities, Fair Value Disclosure	2,059.4		1,875.2				1,908.1	1,544.4			0	330.8
Derivative Liability									$ 1,908.1	$ 1,544.4																																																													$ 1,908.1	$ 1,544.4	$ 151.3
Market value of option																					0.00%	0.00%												50.00%	38.00%														3.00%	4.00%
SWAP rates																					2.00%	2.00%												3.00%	3.00%														2.00%	2.00%
Mortality multiplier																																																	80.00%	80.00%
Surrender rates																					0.50%	0.50%												75.00%	75.00%														7.00%	7.00%
Non-performance spread																																																	0.25%	0.25%																										0.50%	1.50%
Risk margin for uncertainty																																																																														0.50%
Annualized volatility of equity																																																				42.00%
Discount yield																																																				11.00%
Non-cash accretion rate																																					0.00%
Calibration adjustment																								0.00%													1.00%															0.30%