Debt Securities Held for which Other-Than-Temporary Impairment Loss has been Recognized in Current Period or Previously (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Other Than Temporary Impairment Non Credit Losses Recognized In Earnings [Line Items]
Fair Value	$ 46.9	$ 38.3
Amortized Cost Basis	53.2	42.8
Noncredit-related Losses Recognized in OCI	(6.3)	(4.5)
Tax Effect	2.4	1.7
Amount Recorded in OCI	$ (3.9)	$ (2.8)