Investments - Reconciliation of Other than Temporary Impairment on Fixed Maturity (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Investments, Debt and Equity Securities [Abstract]
Document Period End Date	Dec. 31, 2013
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Additions, Additional Credit Losses	$ 0	$ 0
Balance at the beginning of the period	2.7	2.7
Increases attributable to credit losses on securities:
Other-than-temporary impairment was not previously recognized	0	0
Balance at the end of the period	$ 2.7	$ 2.7