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Mortgage Loans by Geographic Region (Detail) (USD $) In Millions, unless otherwise specified | Dec. 31, 2011 | Dec. 31, 2010
--- | --- | ---
Mortgage Loans on Real Estate [Line Items] |  |  |
Mortgage Loans | $ 1,612.3 | [1] | $ 1,516.8
Percent of Total | 100.00% |  | 100.00%
New England |  |  |
Mortgage Loans on Real Estate [Line Items] |  |  |
Mortgage Loans | 147.0 |  | 146.8
Percent of Total | 9.10% |  | 9.70%
Mid-Atlantic |  |  |
Mortgage Loans on Real Estate [Line Items] |  |  |
Mortgage Loans | 174.1 |  | 184.8
Percent of Total | 10.80% |  | 12.20%
East North Central |  |  |
Mortgage Loans on Real Estate [Line Items] |  |  |
Mortgage Loans | 212.7 |  | 171.7
Percent of Total | 13.20% |  | 11.30%
West North Central |  |  |
Mortgage Loans on Real Estate [Line Items] |  |  |
Mortgage Loans | 151.2 |  | 134.6
Percent of Total | 9.40% |  | 8.90%
South Atlantic |  |  |
Mortgage Loans on Real Estate [Line Items] |  |  |
Mortgage Loans | 383.8 |  | 372.0
Percent of Total | 23.80% |  | 24.50%
East South Central |  |  |
Mortgage Loans on Real Estate [Line Items] |  |  |
Mortgage Loans | 52.4 |  | 26.9
Percent of Total | 3.30% |  | 1.80%
West South Central |  |  |
Mortgage Loans on Real Estate [Line Items] |  |  |
Mortgage Loans | 160.4 |  | 171.8
Percent of Total | 9.90% |  | 11.30%
Mountain |  |  |
Mortgage Loans on Real Estate [Line Items] |  |  |
Mortgage Loans | 69.5 |  | 60.7
Percent of Total | 4.30% |  | 4.00%
Pacific |  |  |
Mortgage Loans on Real Estate [Line Items] |  |  |
Mortgage Loans | $ 261.2 |  | $ 247.5
Percent of Total | 16.20% |  | 16.30%
[1] | Amortized cost for fixed maturity securities and mortgage loans represents original cost reduced by repayments, write-downs from other-than-temporary declines in fair value, amortization of premiums, and accretion of discounts.

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- Definition 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. + References 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FASB -Name Statement of Financial Accounting Standard (FAS) -Number 60 -Paragraph 47 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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 SEC -Name Regulation S-X (SX) -Number 210 -Article 7 -Section 03 -Paragraph 1 -Subparagraph c Reference 3: 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 + Details
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