Investments - Amortized Cost and Fair Value of Fixed Maturity Available-for-Sale Securities (Detail) - Other Investments Asset [Member] - Other Invested Assets [Member] - All Other Securities [Member] - USD ($) $ in Millions	Dec. 31, 2015	Sep. 30, 2015
Schedule of Available-for-sale Securities [Line Items]
Trading Securities, Cost	$ 2.5	$ 5.3
Trading Securities	$ 2.5	$ 5.3