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Mortgage Loans Sorted by Applicable Internal Credit Ratings and Loan-to-Value Ratios (Detail) - USD ($) $ in Millions | Mar. 31, 2018 | Dec. 31, 2017
--- | --- | ---
Financing Receivable, Recorded Investment |  |
Mortgage Loans | $ 2,200.8 | $ 2,213.2
Aa Credit Rating |  |
Financing Receivable, Recorded Investment |  |
Mortgage Loans | 0.3 | 0.4
A Credit Rating |  |
Financing Receivable, Recorded Investment |  |
Mortgage Loans | 481.9 | 445.7
Baa Credit Rating |  |
Financing Receivable, Recorded Investment |  |
Mortgage Loans | 1,704.4 | 1,753.0
Ba Credit Rating |  |
Financing Receivable, Recorded Investment |  |
Mortgage Loans | 14.2 | 14.1
Loan to Value Ratio Below or Equal to 65 Percent |  |
Financing Receivable, Recorded Investment |  |
Mortgage Loans | 1,082.6 | 1,101.7
Loan To Value Ratio Above 65 To 75 Percent |  |
Financing Receivable, Recorded Investment |  |
Mortgage Loans | 1,053.8 | 1,041.6
Loan To Value Ratio Above 75 To 85 Percent |  |
Financing Receivable, Recorded Investment |  |
Mortgage Loans | 40.2 | 49.3
Loan To Value Ratio Above 85 Percent |  |
Financing Receivable, Recorded Investment |  |
Mortgage Loans | $ 24.2 | $ 20.6

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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 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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