We are party to derivative contracts through certain of our subsidiaries. The most significant derivative contracts consist of equity index put option contracts. The liabilities and related notional values of these contracts follow (in millions).

Liabilities

Notional

Value

June 30, 2020

1,565

14,348

December 31, 2019

968

14,385

The equity index put option contracts are European style options written prior to March 2008 on four major equity indexes. Notional value in the preceding table represents the aggregate undiscounted amounts payable assuming the value of each index is zero at each contract’s expiration date. Certain contracts are denominated in foreign currencies and the related notional amounts are based on the foreign currency exchange rates as of the balance sheet date. These contracts generated pre-tax gains of $796 million in the second quarter and pre-tax losses of $597 million in the first six months of 2020. Equity index put option contracts produced pre-tax gains of $213 million and $983 million in the second quarter and first six months of 2019, respectively. The losses in the first six months of 2020 reflected declines in index values between December 31, 2019 and June 30, 2020.

Substantially all open contracts as of June 30, 2020 will expire by February 2023. The weighted average life of unexpired contracts at June 30, 2020 was approximately 1.3 years. Future payments, if any, under any given contract will be required if the prevailing index value is below the contract strike price at the expiration date. We received aggregate premiums of $2.5 billion on the contract inception dates with respect to unexpired contracts as of June 30, 2020 and we have no counterparty credit risk. The aggregate intrinsic value (the undiscounted liability assuming the contracts are settled based on the index values and foreign currency exchange rates as of the balance sheet date) was $1.2 billion at June 30, 2020 and $397 million at December 31, 2019. These contracts may not be unilaterally terminated or fully settled before the expiration dates and the ultimate amount of cash basis gains or losses will not be determined until the contract expiration dates.

Our regulated utility subsidiaries are exposed to variations in the prices of fuel required to generate electricity, wholesale electricity purchased and sold and natural gas supplied for customers. We may use forward purchases and sales, futures, swaps and options to manage a portion of these price risks. Most of the net derivative contract assets or liabilities of our regulated utilities are probable of recovery through rates and are offset by regulatory liabilities or assets.