Investments - Amortized Cost and Fair Value of Fixed Maturity Available-for-Sale Securities (Detail) - USD ($) $ in Millions	9 Months Ended
	Jun. 30, 2016	Sep. 30, 2015
Schedule of Available-for-sale Securities [Line Items]
Document Period End Date	Jun. 30, 2016
Total investments, Cost or Amortized Cost	$ 50.7	$ 264.8
Investments, Unrealized Gains	0.0	14.1
Investments, Unrealized Losses	0.0	0.0
Available For Sale Securities Fair Value		278.9
Total investments, Carrying Value	50.7	278.9
Asset based loan receivables [Member]
Schedule of Available-for-sale Securities [Line Items]
Trading Securities, Cost	48.2	226.7
Trading Securities	48.2	226.7
Other Investments Gross Unrealized Gain	0.0	0.0
Other Short Term Investments Gross Unrealized Losses	0.0	0.0
Fixed Maturities Available For Sale [Member] | Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total fixed maturity available-for-sale securities, Amortized Cost		14.1
Total investments, Carrying Value		14.1
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax		0.0
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax		0.0
Other Investments Asset [Member] | Other Invested Assets [Member] | All Other Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Trading Securities, Cost	2.5	5.3
Trading Securities	2.5	5.3
Other Investments Gross Unrealized Gain	0.0	0.0
Other Short Term Investments Gross Unrealized Losses	0.0	0.0
Estimate of Fair Value Measurement [Member]
Schedule of Available-for-sale Securities [Line Items]
Available For Sale Securities Fair Value	50.7
Estimate of Fair Value Measurement [Member] | Asset based loan receivables [Member]
Schedule of Available-for-sale Securities [Line Items]
Trading Securities	48.2	226.7
Estimate of Fair Value Measurement [Member] | Fixed Maturities Available For Sale [Member] | Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Debt Securities		14.1
Estimate of Fair Value Measurement [Member] | Other Investments Asset [Member] | Other Invested Assets [Member] | All Other Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Trading Securities	$ 2.5	5.3
Held for trading [Member] | Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total investments, Carrying Value		32.8
Available-for-sale Equity Securities, Amortized Cost Basis		18.7
Available-for-sale Equity Securities, Accumulated Gross Unrealized Gain, before Tax		14.1
Available-for-sale Equity Securities, Accumulated Gross Unrealized Loss, before Tax		0.0
Held for trading [Member] | Estimate of Fair Value Measurement [Member] | Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Equity Securities		$ 32.8