Mortgage Loans, Sorted by Applicable Credit Quality Indicators, Loan to Value Ratio (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Mortgage Loans on Real Estate [Line Items]
Mortgage Loans	$ 1,776.1	$ 1,712.7
Loan to Value Ratio Below or Equal to 65 Percent
Mortgage Loans on Real Estate [Line Items]
Mortgage Loans	771.8	624.7
Loan To Value Ratio Above 65 To 75 Percent
Mortgage Loans on Real Estate [Line Items]
Mortgage Loans	816.0	858.8
Loan To Value Ratio Above 75 To 85 Percent
Mortgage Loans on Real Estate [Line Items]
Mortgage Loans	121.9	142.5
Loan To Value Ratio Above 85 Percent
Mortgage Loans on Real Estate [Line Items]
Mortgage Loans	$ 66.4	$ 86.7

The balance represents the amount of loans that are secured by real estate mortgages, offset by the reserve to cover probable credit losses on the loan portfolio.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 60

-Paragraph 47

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.1(c))

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 1

-Subparagraph c

-Article 7

Name:	us-gaap_MortgageLoansOnRealEstateCommercialAndConsumerNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant