Revenue recognition   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 long term care contracts are earned ratably over the policy year in which they are due. The reserve for unearned premiums represents the portion of premiums written relating to the unexpired terms of coverage. Insurance receivables include balances due currently or in the future, including amounts due from insureds related to losses under high deductible policies, and are presented at unpaid balances, net of an allowance for doubtful accounts. Amounts are considered past due based on policy payment terms. That allowance is determined based on periodic evaluations of aged receivables, management s experience and current economic conditions. Insurance receivables and any related allowance are written off after collection efforts are exhausted or a negotiated settlement is reached. 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, CNA estimates the amount of ultimate premiums that it 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. CNA 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. Contract drilling revenue from dayrate drilling contracts is recognized as services are performed. In connection with such drilling contracts, Diamond Offshore may receive fees (either lump-sum or dayrate) for the mobilization of equipment. These fees are earned as services are performed ov