Investment and derivative contract gains/losses in the second quarter and first six months of 2021 and 2020 are summarized as follows (in millions).

	Second Quarter						First Six Months
	2021			2020			2021			2020
Investment gains (losses):
Equity securities:
Change in unrealized investment gains (losses) during the period on securities held at the end of the period	$	27,014		$	39,369		$	31,548		$	(18,377	)
Investment gains (losses) on securities sold during the period		144			(87	)		670			(11,233	)
		27,158			39,282			32,218			(29,610	)
Fixed maturity securities:
Gross realized gains		15			25			35			41
Gross realized losses		(12	)		(14	)		(13	)		(20	)
Other		12			(4	)		144			(4	)
Investment gains (losses)		27,173			39,289			32,384			(29,593	)
Derivative contract gains (losses)		221			796			710			(597	)
	$	27,394		$	40,085		$	33,094		$	(30,190	)

Equity securities gains and losses include unrealized gains and losses from changes in fair values during the period on equity securities we still own, as well as gains and losses on securities we sold during the period. As reflected in the Consolidated Statements of Cash Flows, we received proceeds from sales of equity securities of approximately $8.6 billion in the first six months of 2021 and $15.7 billion in the first six months of 2020. In the preceding table, investment gains and losses on equity securities sold during the period reflect the difference between the sales proceeds and the fair value of the equity securities sold at the beginning of the applicable quarterly period or, if later, the purchase date. Our taxable gains/losses on equity securities sold are generally the difference between the proceeds from sales and original cost. Taxable gains in the second quarter and first six months of 2021 were $228 million and $2.0 billion, respectively, and taxable losses were $4.5 billion and $3.3 billion in the second quarter and first six months of 2020, respectively.

The derivative contract gains and losses derive from equity index put option contracts written prior to March 2008 on four major equity indexes. Information related to these contracts follows (dollars in millions).

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. Intrinsic value is the undiscounted liability assuming the contracts are settled based on the index values and foreign currency exchange rates as of the balance sheet date. Substantially all open contracts as of June 30, 2021 will expire by February 2023. Future payments, if any, under any given contract will be required if the prevailing index value is below the contract strike price at the contract expiration date. We received aggregate premiums on the contract inception dates of $1.9 billion with respect to unexpired contracts as of June 30, 2021 and we have no counterparty credit risk.