Impaired Mortgage Loans (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Recorded Investment		$ 17.4
Unpaid Principal Balance		18.9
Related Allowance		1.5
Impaired Fin Receivables with No Related Allowance [Member]
Recorded Investment		4.3
Unpaid Principal Balance		4.3
Related Allowance		0
Impaired Fin Receivables with Allowance [Member]
Recorded Investment	13.1	13.1
Unpaid Principal Balance	14.6	14.6
Related Allowance	$ 1.5	$ 1.5