Future policy benefit reserves for our long term care products and payout annuity contracts and deferred acquisition costs for our long term care products are based on certain assumptions including morbidity, mortality, policy persistency, and discount rates, which are impacted by expected investment yields. The recoverability of deferred acquisition costs and the adequacy of the reserves are contingent on actual experience related to these key assumptions, which were generally established at time of issue. If actual experience differs from these assumptions, the deferred acquisition costs may not be fully realized and the reserves may not be adequate, requiring us to add to reserves. Therefore, our results of operations or equity could be adversely impacted. The inherent risks associated with the reserving process are discussed in the Reserves - Estimates and Uncertainties section below.
The paid development method estimates ultimate losses by reviewing paid loss patterns and applying them to accident years with further expected changes in paid loss. Selection of the paid loss pattern requires consideration of several factors including the impact of inflation on claims costs, the rate at which claims professionals make claim payments and close claims, the impact of judicial decisions, the impact of underwriting changes, the impact of large claim payments and other factors. Claim cost inflation itself requires evaluation of changes in the cost of repairing or replacing property, changes in the cost of medical care, changes in the cost of wage replacement, judicial decisions, legislative changes and other factors. Because this method assumes that losses are paid at a consistent rate, changes in any of these factors can impact the results. Since the method does not rely on case reserves, it is not directly influenced by changes in the adequacy of case reserves.
For CNA Commercial general liability, the most significant factor affecting reserve estimates is claim severity. Claim severity is driven by changes in the cost of repairing or replacing property, the cost of medical care, the cost of wage replacement, judicial decisions, legislation and other factors. If the estimated claim severity for general liability increases by 6%, we estimate that our net reserves would increase by approximately $200 million. If the estimated claim severity for general liability decreases by 3%, we estimate that our net reserves would decrease by approximately $100 million. Our net reserves for CNA Commercial general liability were approximately $3.6 billion at December 31, 2011.
It should be noted that our current GAAP long term care reserves contain a level of margin in excess of management's current best estimates. Any required increase in the net GAAP reserves resulting from the hypothetical revisions in the table below would first reduce the margin before they would impact results of operations. The estimated impact to results of operations in the table below are after consideration of the existing margin.
Favorable net prior year development of $245 million and $344 million was recorded in 2011 and 2010. Further information on CNA Specialty's net prior year development for 2011 and 2010 is included in Note F to the Consolidated Financial Statements included under Item 8.
CNA Specialty's average rate decreased 2% for 2010 and 2009 for policies that renewed in each period. Retention of 86% and 84% was achieved in each period.
Net income improved $236 million in 2010 as compared with 2009. This improvement was primarily due to improved net realized investment results.
Net operating income improved $15 million in 2010 as compared with 2009. This increase was primarily due to increased favorable net prior year development, partially offset by lower net investment income, and higher catastrophe losses.
Unfavorable net prior year development of $6 million was recorded in 2010, and unfavorable net prior year development of $159 million was recorded in 2009 which included $79 million for asbestos exposures and $76 million for environmental pollution exposures. Further information on Corporate & Other Non-Core net prior year development for 2009 is included in Note F to the Consolidated Financial Statements included under Item 8.
Net realized investment gains decreased $50 million for 2011 as compared with 2010. Net realized investment results improved $612 million for 2010 as compared with 2009, driven by significantly lower other-than-temporary impairment (OTTI) losses recognized in earnings. Net realized investment results include OTTI losses of $140 million, $151 million, and $879 million for 2011, 2010, and 2009. Included in the 2009 pretax net realized gains for equity securities was $370 million related to the sale of our holdings of Verisk Analytics, Inc., which began trading on October 7, 2009, after an initial public offering. Since our cost basis in this position was zero, the entire amount was recognized as a pretax realized investment gain. Further information on our realized gains and losses, including our OTTI losses and impairment decision process, is set forth in Note B to the Consolidated Financial Statements included under Item 8. During the second quarter of 2009, the Company adopted updated accounting guidance, which amended the OTTI loss model for fixed maturity securities.
Non-investment grade fixed maturity securities, as presented in the table below, include high-yield securities rated below BBB- by bond rating agencies and other unrated securities that, according to our analysis, are below investment grade. Non-investment grade securities generally involve a greater degree of risk than investment grade securities. The amortized cost of our non-investment grade fixed maturity bond portfolio was $3,200 million and $3,490 million at December 31, 2011 and 2010. The following table summarizes the ratings of this portfolio at fair value.
Premiums: Insurance premiums on property and casualty insurance contracts are recognized in proportion to the underlying risk insured which principally are earned ratably over the duration of the policies. Premiums on accident and health insurance contracts are earned ratably over the policy year in which they are due. The reserve for unearned premiums on these contracts represents the portion of premiums written relating to the unexpired terms of coverage.
Property and casualty contracts that are retrospectively rated contain provisions that result in an adjustment to the initial policy premium depending on the contract provisions and loss experience of the insured during the experience period. For such contracts, the Company estimates the amount of ultimate premiums that the Company may earn upon completion of the experience period and recognizes either an asset or a liability for the difference between the initial policy premium and the estimated ultimate premium. The Company adjusts such estimated ultimate premium amounts during the course of the experience period based on actual results to date. The resulting adjustment is recorded as either a reduction of or an increase to the earned premiums for the period.
Based on current facts and circumstances, the Company has determined that no additional OTTI losses related to the securities in an unrealized loss position presented in the December 31, 2011 Securities in a Gross Unrealized Loss Position table above are required to be recorded. A discussion of some of the factors reviewed in making that determination is presented below.
Level 1 securities include highly liquid U.S. and foreign government bonds, and redeemable preferred stock, valued using quoted market prices. Level 2 securities include most other fixed maturity securities as the significant inputs are observable in the marketplace. Securities are generally assigned to Level 3 in cases where broker/dealer quotes are significant inputs to the valuation and there is a lack of transparency as to whether these quotes are based on information that is observable in the marketplace. Level 3 securities also include tax-exempt and taxable auction rate certificates. Fair value of auction rate securities is determined utilizing a pricing model with three primary inputs. The interest rate and spread inputs are observable from like instruments while the maturity date assumption is unobservable due to the uncertain nature of principal prepayments prior to maturity.
Unfavorable development in workers' compensation was related to increased severity of indemnity losses relative to expectations on claims related to Defense Base Act contractors, primarily in accident years 2008 and prior.
Unfavorable development was recorded related to asbestos. The Company noted adverse development in various asbestos accounts due to increases in average claim severity and defense expense arising from increased trial activity. Additionally, the Company had not seen a decline in the overall emergence of new accounts.
In August 2005, CNAF and certain insurance subsidiaries were joined as defendants, along with other insurers and brokers, in multidistrict litigation pending in the United States District Court for the District of New Jersey, In re Insurance Brokerage Antitrust Litigation, Civil No. 04-5184 (GEB). The plaintiffs' consolidated class action complaint alleged bid rigging and improprieties in the payment of contingent commissions in connection with the sale of insurance. After various motions and preliminary court rulings providing for further proceedings, all parties executed final settlement documents and the plaintiffs filed a motion for preliminary approval of the settlement in May 2011. In June 2011, the Court entered an order preliminarily approving the settlement. A fairness hearing was held in September 2011 to determine final approval of the settlement. The Court took the matter under advisement and will issue a ruling in due course. As currently structured, the settlement will not have a material impact on the Company's results of operations. In addition, the Company does not believe it has any material ongoing exposure relating to this matter.
The CNAF Incentive Compensation Plan (the Plan), as amended and restated on January 1, 2010, authorizes the grant of stock-based compensation to certain management personnel for up to 6 million shares of CNAF's common stock. The Plan currently provides for awards of stock options, stock appreciation rights (SARs), restricted shares, performance-based restricted share units (RSUs) and performance share units. The number of shares available for the granting of stock-based compensation under the Plan as of December 31, 2011 was approximately 2.4 million.