Investments - Net Investment Gains (Losses) (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
Gain (Loss) on Investments [Abstract]
Document Period End Date		Jun. 30, 2013
Net realized gains before other-than-temporary impairments	$ 34.7	$ 280.2	$ 192.0	$ 40.4
Gross other-than-temporary impairments	(0.7)	(1.6)	(21.3)	(2.4)
Non-credit portion of other-than-temporary impairments included in other comprehensive income			1.5	(0.1)
Net realized gains on fixed maturity available-for-sale securities	34.0	278.6	172.2	37.9
Realized gains on equity securities	4.5	6.4	0.8	0.4
Net realized gains on securities	38.5	285.0	173.0	38.3
Realized gains (losses) on certain derivative instruments	54.0	99.3	(32.0)	(26.3)
Unrealized gains on certain derivative instruments	(34.0)	27.3	114.6	(24.9)
Change in fair value of derivatives	20.0	126.6	82.6	(51.2)
Realized gains on other invested assets	(0.2)	(0.1)	(1.0)
Net investment gains (losses)	58.3	411.5	254.6	(12.9)
Other than Temporary Impairment Losses, Investments, Available-for-sale Securities	$ 0.7	$ 1.6	$ 19.8	$ 2.5