Investments - Reconciliation of Other than Temporary Impairment on Fixed Maturity (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Mar. 31, 2013	Apr. 01, 2012	Mar. 31, 2013	Apr. 01, 2012
Investments, Debt and Equity Securities [Abstract]
Balance at the beginning of the period	$ 2.7	$ 2.1	$ 2.7	$ 0.7
Increases attributable to credit losses on securities:
Other-than-temporary impairment was not previously recognized	0	0.5	0	1.9
Balance at the end of the period	$ 2.7	$ 2.6	$ 2.7	$ 2.6