Investments - Other-than-Temporary Impairments (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended		15 Months Ended
	Jun. 30, 2013	Jun. 30, 2013	Jul. 01, 2012	Jul. 01, 2013
Document Period End Date		Jun. 30, 2013
Credit losses in operations, including credit impairments	$ 0.5	$ 0.8
Change-of-intent, and non-credit losses in other comprehensive income		0	2.6	0.7
Other-than-temporary impairments recognized in net income:
Total other-than-temporary impairments	0.7	1.6	19.8	2.5
Credit losses in operations, change of intent operations	0.2	0.9	15.0	1.8
Corporates [Member]
Other-than-temporary impairments recognized in net income:
Total other-than-temporary impairments	0	0	2.2	1.5
Non-agency residential mortgage-backed securities [Member]
Other-than-temporary impairments recognized in net income:
Total other-than-temporary impairments	0.2	1.1	6.9	0.8
Hybrids [Member]
Other-than-temporary impairments recognized in net income:
Total other-than-temporary impairments	0	0	9.7	0
Other Invested Assets [Member]
Other-than-temporary impairments recognized in net income:
Total other-than-temporary impairments	$ 0.5	$ 0.5	$ 1.0	$ 0.2