Investments Mortgage Loan Restructuring (Detail) (Commercial Real Estate Portfolio Segment [Member])	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011
Commercial Real Estate Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Carrying Amount	13.1	9.8
Financing Receivables, modifications, number of contracts	2	1