Investments - Net Investment Income (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
Schedule of Investments [Line Items]
Document Period End Date		Jun. 30, 2013
Gross investment income	$ 193.2	$ 550.2	$ 548.2	$ 182.1
External investment expense	(3.6)	(10.5)	(9.2)	(2.9)
Net investment income	189.6	539.7	539.0	179.2
Fixed maturity available-for-sale securities [Member]
Schedule of Investments [Line Items]
Gross investment income	173.8			172.7
Equity available-for-sale securities [Member]
Schedule of Investments [Line Items]
Gross investment income	3.9	11.5	10.8	4.8
Policy loans [Member]
Schedule of Investments [Line Items]
Gross investment income	0.1	0.6	0.6	0.2
Invested cash and short-term investments [Member]
Schedule of Investments [Line Items]
Gross investment income	0.2	1.4	3.5	2.1
Other investments [Member]
Schedule of Investments [Line Items]
Gross investment income	$ 15.2	$ 29.4	$ 2.9	$ 2.3