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	6 Months Ended				6 Months Ended	12 Months Ended	6 Months Ended							6 Months Ended					6 Months Ended			6 Months Ended			6 Months Ended
	Mar. 31, 2014	Sep. 30, 2013	Mar. 31, 2014 Equity Securities [Member]	Sep. 30, 2013 Equity Securities [Member]	Mar. 31, 2014 Broker Quoted [Member] Municipal Bonds [Member]	Sep. 30, 2013 Option Pricing [Member] Equity Securities [Member]	Mar. 31, 2014 Market pricing [Member] Equity Securities [Member]	Mar. 31, 2014 Broker Quoted [Member] Asset-backed securities [Member]	Sep. 30, 2013 Broker Quoted [Member] Asset-backed securities [Member]	Mar. 31, 2014 Broker Quoted [Member] Commercial mortgage-backed securities [Member]	Sep. 30, 2013 Broker Quoted [Member] Commercial mortgage-backed securities [Member]	Mar. 31, 2014 Broker Quoted [Member] Corporates [Member]	Sep. 30, 2013 Broker Quoted [Member] Corporates [Member]	Mar. 31, 2014 Market pricing [Member] Corporates [Member]	Sep. 30, 2013 Market pricing [Member] Corporates [Member]	Mar. 31, 2014 Market pricing [Member] Municipal Bonds [Member]	Mar. 31, 2014 Contingent purchase price reduction receivable [Member]	Sep. 30, 2013 Contingent purchase price reduction receivable [Member]	Mar. 31, 2014 Contingent purchase price reduction receivable [Member] Discounted cash flow [Member]	Mar. 31, 2014 Fixed Index Annuity [Member]	Sep. 30, 2013 Fixed Index Annuity [Member]	Mar. 31, 2014 Fixed Index Annuity [Member] Discounted cash flow [Member]	Mar. 31, 2014 Equity conversion feature of preferred stock [Member]	Sep. 30, 2013 Equity conversion feature of preferred stock [Member]	Mar. 31, 2014 Equity conversion feature of preferred stock [Member] Monte Carlo simulation / Option model [Member]	Mar. 31, 2014 Minimum [Member] Asset-backed securities [Member]	Mar. 31, 2013 Minimum [Member] Asset-backed securities [Member]	Mar. 31, 2014 Minimum [Member] Corporates [Member]	Mar. 31, 2013 Minimum [Member] Corporates [Member]	Mar. 31, 2013 Minimum [Member] Hybrids [Member]	Mar. 31, 2014 Minimum [Member] Equity Securities [Member]	Mar. 31, 2014 Minimum [Member] Contingent purchase price reduction receivable [Member]	Mar. 31, 2013 Minimum [Member] Contingent purchase price reduction receivable [Member]	Mar. 31, 2014 Minimum [Member] Fixed Index Annuity [Member]	Mar. 31, 2013 Minimum [Member] Fixed Index Annuity [Member]	Mar. 31, 2014 Minimum [Member] Equity conversion feature of preferred stock [Member]	Mar. 31, 2013 Minimum [Member] Equity conversion feature of preferred stock [Member]	Mar. 31, 2014 Maximum [Member] Asset-backed securities [Member]	Mar. 31, 2013 Maximum [Member] Asset-backed securities [Member]	Mar. 31, 2013 Maximum [Member] Commercial mortgage-backed securities [Member]	Mar. 31, 2014 Maximum [Member] Corporates [Member]	Mar. 31, 2013 Maximum [Member] Corporates [Member]	Mar. 31, 2013 Maximum [Member] Hybrids [Member]	Mar. 31, 2014 Maximum [Member] Equity Securities [Member]	Mar. 31, 2014 Maximum [Member] Contingent purchase price reduction receivable [Member]	Mar. 31, 2013 Maximum [Member] Contingent purchase price reduction receivable [Member]	Mar. 31, 2014 Maximum [Member] Fixed Index Annuity [Member]	Mar. 31, 2013 Maximum [Member] Fixed Index Annuity [Member]	Mar. 31, 2014 Maximum [Member] Equity conversion feature of preferred stock [Member]	Mar. 31, 2013 Maximum [Member] Equity conversion feature of preferred stock [Member]	Mar. 31, 2014 Weighted Average [Member]	Mar. 31, 2014 Weighted Average [Member] Asset-backed securities [Member]	Mar. 31, 2013 Weighted Average [Member] Asset-backed securities [Member]	Mar. 31, 2014 Weighted Average [Member] Commercial mortgage-backed securities [Member]	Mar. 31, 2014 Weighted Average [Member] Corporates [Member]	Mar. 31, 2013 Weighted Average [Member] Corporates [Member]	Mar. 31, 2014 Weighted Average [Member] Municipal Debt Securities [Member]	Mar. 31, 2014 Weighted Average [Member] Hybrids [Member]	Mar. 31, 2013 Weighted Average [Member] Hybrids [Member]	Mar. 31, 2014 Weighted Average [Member] Equity Securities [Member]	Mar. 31, 2014 Weighted Average [Member] Contingent purchase price reduction receivable [Member]	Mar. 31, 2013 Weighted Average [Member] Contingent purchase price reduction receivable [Member]	Mar. 31, 2014 Weighted Average [Member] Fixed Index Annuity [Member]	Mar. 31, 2013 Weighted Average [Member] Fixed Index Annuity [Member]	Mar. 31, 2014 Weighted Average [Member] Equity conversion feature of preferred stock [Member]	Mar. 31, 2013 Weighted Average [Member] Equity conversion feature of preferred stock [Member]	Mar. 31, 2014 Front Street Future Policyholder Benefits Reserve [Member] Minimum [Member]	Mar. 31, 2014 Front Street Future Policyholder Benefits Reserve [Member] Maximum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Document Period End Date	Mar. 31, 2014
Valuation Technique					Broker-quoted	Option Pricing	Market Pricing	Broker-quoted						Market Pricing					Discounted cash flow			Discounted cash flow			Monte Carlo simulation / Option model
Assets, Fair Value Disclosure	$ 755.6	$ 523.5	$ 10.8	$ 10.7				$ 10.7	$ 5.0	$ 0	$ 5.7	$ 591.2	$ 404.5	$ 65.8	$ 56.6	$ 35.6	$ 41.5	$ 41.0
Probability of collection																																88.00%	88.00%												96.00%	96.00%															92.00%	92.00%
Expected term																																													6 months	9 months
Discount rate																																													1.00%	1.00%
Credit insurance risk premium																																													12.00%	11.00%
Quoted prices																												0.00%	0.00%												138.00%	113.00%													94.00%	90.00%			0.00%
Offered quotes																										96.00%	100.00%	94.00%	90.00%									101.00%	107.00%	96.00%	120.00%	131.00%										99.00%	101.00%	0.00%	99.00%	97.00%	102.00%	25.00%
Fair Value Inputs, Risk-free Discount Factor																																																			0.999
Fair Value Inputs, Risk-adjusted Discount Factor																																																			0.995
Fair Value Inputs, Upward Movement																																																			1.1
Fair Value Inputs, Downward Movement																																																			0.9
Fair Value Inputs, Probability of Upward Movement																																																			48.60%
Fair Value Inputs, Probability of Downward Movement																																																			51.40%
Liabilities
Liabilities, Fair Value Disclosure	$ 2,234.5	$ 1,875.2																		$ 1,718.7	$ 1,544.4		$ 364.8	$ 330.8
Market value of option																																		0.00%	0.00%												44.00%	38.00%															4.00%	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%															0.25%	0.25%			0.60%	1.50%
Risk margin for uncertainty																																																																			0.30%	0.50%
Annualized volatility of equity																																																																	41.00%	42.00%
Discount yield																																																																	11.00%	11.00%
Non-cash accretion rate																																																	0.00%	0.00%
Calibration adjustment																																				0.00%	0.00%												1.00%	1.00%															0.00%	0.30%
Fair Value Measurements Revenue Multiple																															0.3													0.4
Fair Value Measurements Probability of Transaction																																																												90.00%