Investments in equity securities - Narrative (Detail) - Investment Commitment [Member] - USD ($) $ / shares in Units, $ in Billions		12 Months Ended
	Apr. 30, 2019	Dec. 31, 2019
Summary of Investment Holdings [Line Items]
Investment commitment description		On April 30, 2019, Berkshire committed to invest a total of $10 billion in connection with Occidental Petroleum Corporation’s (“Occidental”) proposal to acquire Anadarko Petroleum Corporation (“Anadarko”). The Anadarko shareholders approved the acquisition by Occidental on August 8, 2019 and the acquisition and our investment in Occidental closed on August 8, 2019. Our investments in Occidental are included in the commercial, industrial and other category in the preceding table. Berkshire’s investments in Occidental include newly issued Occidental Cumulative Perpetual Preferred Stock with an aggregate liquidation value of $10 billion, together with warrants to purchase up to 80 million shares of Occidental common stock at an exercise price of $62.50 per share. The preferred stock accrues dividends at 8% per annum and is redeemable at the option of Occidental commencing on the tenth anniversary of issuance at a redemption price equal to 105% of the liquidation preference plus any accumulated and unpaid dividends, or mandatorily under certain specified capital return events. Dividends on the preferred stock may be paid in cash or, at Occidental’s option, in shares of Occidental common stock. The warrants are exercisable in whole or in part until one year after the redemption of the preferred stock.
Occidental Petroleum Corporation [Member] | Cumulative Perpetual Preferred Stock and Warrants [Member]
Summary of Investment Holdings [Line Items]
Investment commitment amount	$ 10
Occidental Petroleum Corporation [Member] | Cumulative Perpetual Preferred Stock [Member]
Summary of Investment Holdings [Line Items]
Investment in preferred stock, liquidation value	$ 10
Investment in preferred stock, stated dividend rate	8.00%
Investment in preferred stock, period from issuance date to redemption period start date	10 years
Investment in preferred stock, redemption price percentage of liquidation preference	105.00%
Occidental Petroleum Corporation [Member] | Common Stock [Member]
Summary of Investment Holdings [Line Items]
Number of common shares that can be purchased	80,000,000
Exercise price for warrants, per share	$ 62.50