<?xml version="1.0" encoding="us-ascii"?><InstanceReport xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"><Version>2.4.0.8</Version><ReportLongName>2114100 - Disclosure - Debt</ReportLongName><DisplayLabelColumn>true</DisplayLabelColumn><ShowElementNames>false</ShowElementNames><RoundingOption /><HasEmbeddedReports>false</HasEmbeddedReports><Columns><Column FlagID="0"><Id>1</Id><IsAbstractGroupTitle>false</IsAbstractGroupTitle><LabelSeparator>

</LabelSeparator><CurrencyCode /><FootnoteIndexer /><hasSegments>false</hasSegments><hasScenarios>false</hasScenarios><MCU><KeyName /><CurrencySymbol /><contextRef><ContextID>D2012Q4YTD</ContextID><EntitySchema>http://www.sec.gov/CIK</EntitySchema><EntityValue>0000045947</EntityValue><PeriodDisplayName /><PeriodType>duration</PeriodType><PeriodStartDate>2012-01-01T00:00:00</PeriodStartDate><PeriodEndDate>2012-12-31T00:00:00</PeriodEndDate><Segments /><Scenarios /></contextRef><UPS /><CurrencyCode /><OriginalCurrencyCode /></MCU><CurrencySymbol /><Labels><Label Key="CalendarSupplement" Id="0" Label="12 Months Ended" /><Label Key="Calendar" Id="1" Label="Dec. 31, 2012" /></Labels></Column></Columns><Rows><Row FlagID="0"><Id>1</Id><IsAbstractGroupTitle>true</IsAbstractGroupTitle><LabelSeparator>

</LabelSeparator><Level>1</Level><ElementName>us-gaap_DebtDisclosureAbstract</ElementName><ElementPrefix>us-gaap_</ElementPrefix><IsBaseElement>true</IsBaseElement><BalanceType>na</BalanceType><PeriodType>duration</PeriodType><IsReportTitle>false</IsReportTitle><IsSegmentTitle>false</IsSegmentTitle><IsCalendarTitle>false</IsCalendarTitle><IsEquityPrevioslyReportedAsRow>false</IsEquityPrevioslyReportedAsRow><IsEquityAdjustmentRow>false</IsEquityAdjustmentRow><IsBeginningBalance>false</IsBeginningBalance><IsEndingBalance>false</IsEndingBalance><IsReverseSign>false</IsReverseSign><FootnoteIndexer /><Cells><Cell FlagID="0" ContextID="" UnitID=""><Id>1</Id><IsNumeric>false</IsNumeric><IsRatio>false</IsRatio><DisplayZeroAsNone>false</DisplayZeroAsNone><NumericAmount>0</NumericAmount><RoundedNumericAmount>0</RoundedNumericAmount><NonNumbericText /><FootnoteIndexer /><CurrencyCode /><CurrencySymbol /><IsIndependantCurrency>false</IsIndependantCurrency><ShowCurrencySymbol>false</ShowCurrencySymbol><DisplayDateInUSFormat>false</DisplayDateInUSFormat></Cell></Cells><ElementDataType>xbrli:stringItemType</ElementDataType><SimpleDataType>string</SimpleDataType><IsTotalLabel>false</IsTotalLabel><UnitID>0</UnitID><Label>Debt Disclosure [Abstract]</Label></Row><Row FlagID="0"><Id>2</Id><IsAbstractGroupTitle>false</IsAbstractGroupTitle><LabelSeparator>

</LabelSeparator><Level>2</Level><ElementName>us-gaap_DebtDisclosureTextBlock</ElementName><ElementPrefix>us-gaap_</ElementPrefix><IsBaseElement>true</IsBaseElement><BalanceType>na</BalanceType><PeriodType>duration</PeriodType><IsReportTitle>false</IsReportTitle><IsSegmentTitle>false</IsSegmentTitle><IsCalendarTitle>false</IsCalendarTitle><IsEquityPrevioslyReportedAsRow>false</IsEquityPrevioslyReportedAsRow><IsEquityAdjustmentRow>false</IsEquityAdjustmentRow><IsBeginningBalance>false</IsBeginningBalance><IsEndingBalance>false</IsEndingBalance><IsReverseSign>false</IsReverseSign><PreferredLabelRole>verboseLabel</PreferredLabelRole><FootnoteIndexer /><Cells><Cell FlagID="0" ContextID="D2012Q4YTD" UnitID=""><Id>1</Id><IsNumeric>false</IsNumeric><IsRatio>false</IsRatio><DisplayZeroAsNone>false</DisplayZeroAsNone><NumericAmount>0</NumericAmount><RoundedNumericAmount>0</RoundedNumericAmount><NonNumbericText>&lt;div style="font-family:Times New Roman;font-size:10pt;"&gt;&lt;div style="line-height:120%;padding-top:18px;font-size:11pt;"&gt;&lt;font style="font-family:inherit;font-size:11pt;font-weight:bold;"&gt;Debt&lt;/font&gt;&lt;/div&gt;&lt;div style="line-height:120%;padding-bottom:6px;padding-top:6px;text-align:left;font-size:10pt;"&gt;&lt;font style="font-family:inherit;font-size:10pt;font-weight:bold;"&gt;Collateralized Advances &lt;/font&gt;&lt;/div&gt;&lt;div style="line-height:120%;padding-bottom:6px;padding-top:6px;text-align:left;font-size:10pt;"&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt;The Company became a member of the Federal Home Loan Bank of Boston (&amp;#8220;FHLBB&amp;#8221;) in May 2011. Membership allows the Company access to collateralized advances, which may be used to support various spread-based business and enhance liquidity management. The Connecticut Department of Insurance (&amp;#8220;CTDOI&amp;#8221;) will permit the Company to pledge up to &lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;color:#000000;text-decoration:none;"&gt;$1.25 billion&lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt; in qualifying assets to secure FHLBB advances for 2013. The amount of advances that can be taken are dependent on the asset types pledged to secure the advances. The pledge limit is recalculated annually based on statutory admitted assets and capital and surplus. The Company would need to seek the prior approval of the CTDOI if there were a desire to exceed these limits. As of December 31, 2012, the Company had &lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;color:#000000;text-decoration:none;"&gt;no&lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt; advances outstanding under the FHLBB facility. &lt;/font&gt;&lt;/div&gt;&lt;div style="line-height:120%;padding-bottom:6px;padding-top:6px;text-align:left;font-size:10pt;"&gt;&lt;font style="font-family:inherit;font-size:10pt;font-weight:bold;"&gt;Consumer Notes &lt;/font&gt;&lt;/div&gt;&lt;div style="line-height:120%;padding-bottom:6px;padding-top:6px;text-align:left;font-size:10pt;"&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt;The Company issued consumer notes through its Retail Investor Notes Program prior to 2009. A consumer note is an investment product distributed through broker-dealers directly to retail investors as medium-term, publicly traded fixed or floating rate, or a combination of fixed and floating rate, notes. Consumer notes are part of the Company&amp;#8217;s spread-based business and proceeds are used to purchase investment products, primarily fixed rate bonds. Proceeds are not used for general operating purposes. Consumer notes maturities may extend up to &lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;color:#000000;text-decoration:none;"&gt;30 years&lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt; and have contractual coupons based upon varying interest rates or indexes (e.g. consumer price index) and may include a call provision that allows the Company to extinguish the notes prior to its scheduled maturity date. Certain Consumer notes may be redeemed by the holder in the event of death. Redemptions are subject to certain limitations, including calendar year aggregate and individual limits. The aggregate limit is equal to the greater of &lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;color:#000000;text-decoration:none;"&gt;$1&lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt; or &lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;color:#000000;text-decoration:none;"&gt;1%&lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt; of the aggregate principal amount of the notes as of the end of the prior year. The individual limit is &lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;color:#000000;text-decoration:none;"&gt;$250&lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt; thousand per individual. Derivative instruments are utilized to hedge the Company&amp;#8217;s exposure to market risks in accordance with Company policy. &lt;/font&gt;&lt;/div&gt;&lt;div style="line-height:120%;padding-bottom:6px;padding-top:6px;text-align:left;font-size:10pt;"&gt;&lt;font style="font-family:inherit;font-size:10pt;color:#000000;text-decoration:none;"&gt;As of December 31, 2012&lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt;, these consumer notes have interest rates ranging from &lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;color:#000000;text-decoration:none;"&gt;4%&lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt; to &lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;color:#000000;text-decoration:none;"&gt;6%&lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt; for fixed notes and, for variable notes, based on &lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;color:#000000;text-decoration:none;"&gt;December&amp;#160;31, 2012&lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt; rates, either consumer price index plus &lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;color:#000000;text-decoration:none;"&gt;100&lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt; to &lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;color:#000000;text-decoration:none;"&gt;260&lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt; basis points, or indexed to the S&amp;amp;P 500, Dow Jones Industrials, foreign currency, or the Nikkei 225. The aggregate maturities of Consumer Notes are as follows: &lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;color:#000000;text-decoration:none;"&gt;$78&lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt; in 2013, &lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;color:#000000;text-decoration:none;"&gt;$13&lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt; in 2014, &lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;color:#000000;text-decoration:none;"&gt;$30&lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt; in 2015, &lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;color:#000000;text-decoration:none;"&gt;$18&lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt; in 2016, &lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;color:#000000;text-decoration:none;"&gt;$12&lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt; in 2017 and &lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;color:#000000;text-decoration:none;"&gt;$8&lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt; thereafter. For 2012, 2011 and 2010, interest credited to holders of consumer notes was &lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;color:#000000;text-decoration:none;"&gt;$10&lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt;, &lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;color:#000000;text-decoration:none;"&gt;$15&lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt; and &lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;color:#000000;text-decoration:none;"&gt;$25&lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt;, respectively.&lt;/font&gt;&lt;/div&gt;&lt;/div&gt;</NonNumbericText><FootnoteIndexer /><CurrencyCode /><CurrencySymbol /><IsIndependantCurrency>false</IsIndependantCurrency><ShowCurrencySymbol>false</ShowCurrencySymbol><DisplayDateInUSFormat>false</DisplayDateInUSFormat></Cell></Cells><ElementDataType>nonnum:textBlockItemType</ElementDataType><SimpleDataType>na</SimpleDataType><ElementDefenition>The entire disclosure for information about short-term and long-term debt arrangements, which includes amounts of borrowings under each line of credit, note payable, commercial paper issue, bonds indenture, debenture issue, own-share lending arrangements and any other contractual agreement to repay funds, and about the underlying arrangements, rationale for a classification as long-term, including repayment terms, interest rates, collateral provided, restrictions on use of assets and activities, whether or not in compliance with debt covenants, and other matters important to users of the financial statements, such as the effects of refinancing and noncompliance with debt covenants.</ElementDefenition><ElementReferences>Reference 1: http://www.xbrl.org/2003/role/presentationRef

 -Publisher FASB

 -Name Accounting Standards Codification

 -Topic 505

 -SubTopic 10

 -Section 50

 -Paragraph 3

 -URI http://asc.fasb.org/extlink&amp;oid=6928386&amp;loc=d3e21475-112644



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

 -Publisher SEC

 -Name Regulation S-X (SX)

 -Number 210

 -Section 02

 -Paragraph 19, 20, 22

 -Article 5



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

 -Publisher FASB

 -Name Statement of Financial Accounting Standard (FAS)

 -Number 129

 -Paragraph 2, 4

 -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 4: http://www.xbrl.org/2003/role/presentationRef

 -Publisher FASB

 -Name Accounting Standards Codification

 -Topic 210

 -SubTopic 10

 -Section S99

 -Paragraph 1

 -Subparagraph (SX 210.5-02.19,20,22)

 -URI http://asc.fasb.org/extlink&amp;oid=6877327&amp;loc=d3e13212-122682



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