NOTES TO CONSOLIDATED FINANCIAL STATEMENTS The amortized cost and fair value of fixed maturities by contractual maturity as of December 31,
## Table 0 ##
Expected maturities may differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties.
For categorization purposes, Aon considers any rating of Baa or higher by Moody’s Investor Services or equivalent rating agency to be investment grade.
Aon’s continuing operations have no fixed maturities with an unrealized loss at December 31, 2007.
Aon’s fixed-maturity portfolio is subject to interest rate, market and credit risks.
With a carrying value of approximately $150 million at December 31, 2007, Aon’s total fixed-maturity portfolio is approximately 96% investment grade based on market value.
Aon’s non publicly-traded fixed maturity portfolio had a carrying value of $9 million.
Valuations of these securities primarily reflect the fundamental analysis of the issuer and current market price of comparable securities.
Aon’s equity portfolio is comprised of a preferred stock not publicly traded.
This portfolio is subject to interest rate, market, credit, illiquidity, concentration and operational performance risks.
Limited Partnership Securitization.
In 2001, Aon sold the vast majority of its limited partnership (LP) portfolio, valued at $450 million, to PEPS I, a QSPE.
The common stock interest in PEPS I is held by a limited liability company which is owned by Aon (49%) and by a charitable trust, which is not controlled by Aon, established for victims of September 11 (51%).
Approximately $171 million of investment grade fixed-maturity securities were sold by PEPS I to unaffiliated third parties.
PEPS I then paid Aon’s insurance underwriting subsidiaries the $171 million in cash and issued to them an additional $279 million in fixed-maturity and preferred stock securities.
As part of this transaction, Aon is required to purchase from PEPS I additional fixed-maturity securities in an amount equal to the unfunded limited partnership commitments, as they are requested.
Aon funded $2 million of commitments in both 2007 and 2006.
As of December 31, 2007, these unfunded commitments amounted to $44 million.
These commitments have specific expiration dates and the general partners may decide not to draw on these commitments.
The carrying value of the PEPS I preferred stock was $168 million and $210 million at December 31, 2007 and 2006, respectively.
Prior to 2007, income distributions received from PEPS I were limited to interest payments on various PEPS I debt instruments.
Beginning in 2007, PEPS I had redeemed or collateralized all of its debt, and as a result, began to pay preferred income distributions.
In 2007, the Company received $61 million of income distributions from PEPS I, which are included in investment income.
to 18 months after the end of each contract year to which it applies.
We defer the recognition of any revenues for favorable contingent underwriting fee adjustments related to cost underruns until the amount is determinable and the collectibility is reasonably assured.
We estimate and recognize unfavorable contingent underwriting fee adjustments related to cost overruns currently in operations as an increase in benefit expenses.
We continually review these benefit expense estimates of future payments to the government for cost overruns and make necessary adjustments to our reserves.
The military services contracts contain provisions to negotiate change orders.
Change orders occur when we perform services or incur costs under the directive of the federal government that were not originally specified in our contract.
Under federal regulations we may be entitled to an equitable adjustment to the contract price in these situations.
Change orders may be negotiated and settled at any time throughout the year.
We record revenue applicable to change orders when services are performed and these amounts are determinable and the collectibility is reasonably assured.
Investment Securities Investment securities totaled $7,497.2 million, or 53% of total assets at December 31, 2009, and $5,215.4 million, or 40% of total assets at December 31, 2008.
Debt securities, detailed below, comprised this entire investment portfolio at December 31, 2009 and over 99% of this investment portfolio at December 31, 2008.
The fair value of debt securities were as follows at December 31, 2009 and 2008:
## Table 1 ##
Approximately 99% of our debt securities were investment-grade quality, with an average credit rating of AA+ by S&P at December 31, 2009.
Most of the debt securities that are below investment-grade are rated BB or better, the higher end of the below investment-grade rating scale.
Our investment policy limits investments in a single issuer and requires diversification among various asset types.
Tax exempt municipal securities included pre-refunded bonds of $346.9 million at December 31, 2009 and $694.8 million at December 31, 2008.
These pre-refunded bonds are secured by an escrow fund consisting of U. S.  government obligations sufficient to pay off all amounts outstanding at maturity.
The ratings of these pre-refunded bonds generally assume the rating of the government obligations (AAA by S&P) at the time the fund is established.
In addition, certain monoline insurers guarantee the timely repayment of bond principal and interest when a bond issuer defaults and generally provide credit enhancement for bond issues related to our tax exempt municipal securities.
We have no direct exposure to these monoline insurers.
We owned $587.2 million and $452.4 million at December 31, 2009 and 2008, respectively, of tax exempt securities guaranteed by monoline insurers.
The equivalent S&P credit rating of these tax-exempt securities without the guarantee from the monoline insurer was AA-.
Humana Inc.  NOTES TO CONSOLIDATED FINANCIAL STATEMENTS—(Continued) 108 6.
MEDICARE PART D As discussed in Note 2, we cover prescription drug benefits in accordance with Medicare Part D under multiple contracts with CMS.
The accompanying consolidated balance sheets include the following amounts associated with Medicare Part D as of December 31, 2015 and 2014.
CMS subsidies/discounts in the table below include the reinsurance and low-income cost subsidies funded by CMS for which we assume no risk as well as brand name prescription drug discounts for Part D plan participants in the coverage gap funded by CMS and pharmaceutical manufacturers.
## Table 2 ##
7.
HEALTH CARE REFORM Operating results for our individual commercial medical business compliant with the Health Care Reform Law have been challenged primarily due to unanticipated modifications in the program subsequent to the passing of the Health Care Reform Law, resulting in higher covered population morbidity and the ensuing enrollment and claims issues causing volatility in claims experience.
We took a number of actions in 2015 to improve the profitability of our individual commercial medical business in 2016.
These actions were subject to regulatory restrictions in certain geographies and included premium increases for the 2016 coverage year related generally to the first half of 2015 claims experience, the discontinuation of certain products as well as exit of certain markets for 2016, network improvements, enhancements to claims and clinical processes and administrative cost control.
Despite these actions, the deterioration in the second half of 2015 claims experience together with 2016 open enrollment results indicating the retention of many high-utilizing members for 2016 resulted in a probable future loss.
As a result of our assessment of the profitability of our individual medical policies compliant with the Health Care Reform Law, in the fourth quarter of 2015, we recorded a provision for probable future losses (premium deficiency reserve) for the 2016 coverage year of $176 million in benefits payable in our consolidated balance sheet with a corresponding increase in benefits expense in our consolidated statement of income.
The premium deficiency reserve includes the estimated benefit of approximately $340 million associated with risk corridor provisions expected for the 2016 coverage year.
On June 30, 2015 we received notification from CMS of risk adjustment and reinsurance settlement amounts for 2014.
We revised our 2014 coverage year estimates to reflect actual amounts and also made a corresponding adjustment to our risk corridor estimate based on these results.
The change in estimate for risk adjustment was substantially offset by the corresponding change in estimate for risk corridor, both of which are reflected as changes in premiums revenue in our consolidated statements of income.
The change in estimate related to the 3Rs for the 2014 coverage year was a decline in the estimated net receivable of approximately $43 million for the year ended December 31, 2015.
In addition, we revised our 3Rs estimates for the 2015 coverage year based on the data from CMS for 2014.
During the year ended December 31, 2015, we paid $186 million in risk adjustment charges and $1 million in risk corridor charges associated with the 2014 coverage year.
We received payments of $521 million for reinsurance recoverables, $57 million for risk adjustment settlements, and $26 million for risk corridor settlements associated with the 2014 coverage year during the year ended December 31, 2015.
We expect to collect the remaining risk adjustment receivable for the 2014 coverage year of approximately $4 million in 2016.
During 2015, we received our interim settlement associated with our risk corridor receivables for the 2014 coverage year.
The interim settlement, representing only 12.6% of risk corridor receivables for the 2014 coverage year, was funded by HHS in accordance with previous guidance, utilizing funds HHS collected from us and other carriers under the 2014 risk corridor program.
As discussed in Note 2, HHS provided guidance under the three year risk corridor program that future collections will first be applied to any shortfalls from previous coverage years before application

<table><tr><td>(millions)</td><td>AmortizedCost</td><td>FairValue</td></tr><tr><td>Due in one year or less</td><td>$50</td><td>$50</td></tr><tr><td>Due after one year through five years</td><td>52</td><td>52</td></tr><tr><td>Due after five years through ten years</td><td>47</td><td>47</td></tr><tr><td>Due after ten years</td><td>1</td><td>1</td></tr><tr><td>Total fixed maturities</td><td>$150</td><td>$150</td></tr></table>
<table><tr><td></td><td> December 31, 2009</td><td>Percentage of Total</td><td> December 31, 2008</td><td> Percentage of Total</td></tr><tr><td></td><td colspan="4"> (dollars in thousands)</td></tr><tr><td>U.S. Treasury and other U.S. government corporations and agencies:</td><td></td><td></td><td></td><td></td></tr><tr><td>U.S. Treasury and agency obligations</td><td>$1,009,352</td><td>13.5%</td><td>$599,898</td><td>11.5%</td></tr><tr><td>Mortgage-backed securities</td><td>1,688,663</td><td>22.5%</td><td>1,297,705</td><td>24.9%</td></tr><tr><td>Tax-exempt municipal securities</td><td>2,224,041</td><td>29.7%</td><td>1,689,462</td><td>32.5%</td></tr><tr><td>Mortgage-backed securities:</td><td></td><td></td><td></td><td></td></tr><tr><td>Residential</td><td>95,412</td><td>1.3%</td><td>347,308</td><td>6.7%</td></tr><tr><td>Commercial</td><td>279,626</td><td>3.7%</td><td>260,299</td><td>5.0%</td></tr><tr><td>Asset-backed securities</td><td>107,188</td><td>1.4%</td><td>144,370</td><td>2.8%</td></tr><tr><td>Corporate debt securities</td><td>2,079,568</td><td>27.7%</td><td>855,827</td><td>16.4%</td></tr><tr><td>Redeemable preferred stock</td><td>13,300</td><td>0.2%</td><td>10,050</td><td>0.2%</td></tr><tr><td>Total debt securities</td><td>$7,497,150</td><td>100.0%</td><td>$5,204,919</td><td>100.0%</td></tr></table>
<table><tr><td></td><td colspan="2">2015</td><td colspan="2">2014</td></tr><tr><td></td><td>RiskCorridorSettlement</td><td>CMSSubsidies/Discounts</td><td>RiskCorridorSettlement</td><td>CMSSubsidies/Discounts</td></tr><tr><td></td><td colspan="4">(in millions)</td></tr><tr><td>Other current assets</td><td>$25</td><td>$2,082</td><td>$105</td><td>$1,690</td></tr><tr><td>Trade accounts payable and accrued expenses</td><td>-47</td><td>-63</td><td>-36</td><td>-32</td></tr><tr><td>Net current (liability) asset</td><td>$-22</td><td>$2,019</td><td>$69</td><td>$1,658</td></tr></table>

Question: What is the ratio of Mortgage-backed securities to the total in 2009? (in %)
Answer: 22.5