Impaired Mortgage Loans (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Recorded Investment	$ 14.0	$ 22.5
Unpaid Principal Balance	15.5	24.0
Related Allowance	1.5	1.5
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
Impaired Fin Receivables with No Related Allowance [Member]
Recorded Investment	0.9	9.4
Unpaid Principal Balance	0.9	9.4
Related Allowance	$ 0	$ 0