Put option contracts

I am trying to understand put option contracts. Some useful links

From the last link comes this:

Berkshire has written equity index put option contracts on four major equity indexes including three indexes outside of the United States. These contracts are European style options and will be settled on the contract expiration dates, which occur between September 2019 and January 2028. Future payments, if any, under these contracts will be required if the underlying index value is below the strike price at the contract expiration dates. Premiums on these contracts were received in full at the contract inception dates and therefore Berkshire has no counterparty credit risk. At March 31, 2009, the aggregate intrinsic value (the undiscounted liability assuming the contracts are settled on their future expiration dates based on the March 31, 2009 index values) was $13.3 billion. However, these contracts may not be terminated or fully settled before the expiration dates and therefore the ultimate amount of cash basis gains or losses on these contracts will not be known for many years.

Credit default contracts include various high yield indexes, state/municipal debt issuers and individual corporation issuers. These contracts cover the loss in value of specified debt obligations of the issuers arising from default events, which are usually for non-payment or bankruptcy. Loss amounts are subject to contract limits.

High yield indexes are comprised of specified North American corporate issuers (usually 100 in number) whose obligations are rated below investment grade. The weighted average contract duration at March 31, 2009 was approximately 2 years. State and municipality contracts are comprised of over 500 reference obligations issuers, which had a weighted average duration at March 31, 2009 of approximately 12 years. Risks related to approximately 50% of the municipality notional amount cannot be settled before the maturity dates of the underlying obligations, which range from 2019 to 2054.

Premiums on the high yield index and state/municipality contracts were received in full at the inception dates of the contracts and, as a result, Berkshire has no counterparty credit risk. Berkshire’s payment obligations under certain of these contracts are on a first loss basis. Several other contracts are subject to aggregate loss deductibles that must be satisfied before Berkshire has any payment obligations.

Credit default contracts written on individual corporate issuers in North America primarily relate to investment grade obligations. Installment premiums are due from counterparties over the terms of the contracts. In most instances, premiums are due from counterparties on a quarterly basis. Most individual issuer contracts expire in 2013.

With limited exception, Berkshire’s equity index put option and credit default contracts contain no collateral posting requirements with respect to changes in either the fair value or intrinsic value of the contracts and/or a downgrade of Berkshire’s credit rating. Under certain conditions, a few contracts require that Berkshire post collateral. As of March 31, 2009, Berkshire’s collateral posting requirement under such contracts was approximately $1 billion.