Condensed Financial Information - Statements of Earnings and Comprehensive Income (Detail) - USD ($) $ in Millions	3 Months Ended																12 Months Ended
	Dec. 31, 2020		Sep. 30, 2020		Jun. 30, 2020		Mar. 31, 2020		Dec. 31, 2019		Sep. 30, 2019		Jun. 30, 2019		Mar. 31, 2019		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
From consolidated subsidiaries:
Investment gains (losses)																	$ 40,905	$ 71,123	$ (22,155)
Equity method earnings (losses)																	726	1,176	(2,167)
Total revenues	$ 64,381		$ 63,024		$ 56,840		$ 61,265		$ 65,368		$ 64,972		$ 63,598		$ 60,678		245,510	254,616	247,837
Cost and expense items:
Interest expense																	4,083	3,961	3,853
Income tax expense (benefit)																	12,440	20,904	(321)
Total costs and expenses																	231,289	225,703	219,214
Net earnings attributable to Berkshire Hathaway shareholders	$ 35,835	[1]	$ 30,137	[1]	$ 26,295	[1]	$ (49,746)	[1]	$ 29,159	[1]	$ 16,524	[1]	$ 14,073	[1]	$ 21,661	[1]	42,521	81,417	4,021
Other comprehensive income, net																	1,000	(228)	(2,211)
Comprehensive income attributable to Berkshire Hathaway shareholders																	43,521	81,189	1,810
Berkshire Hathaway Inc. (Parent) [Member]
From consolidated subsidiaries:
Dividends and distributions																	26,110	15,603	9,658
Undistributed earnings (losses)																	17,402	65,237	(3,952)
Total income from consolidated subsidiaries																	43,512	80,840	5,706
Investment gains (losses)																	(24)	(125)	(4)
Equity method earnings (losses)																	95	493	(2,730)
Other income																	328	780	649
Total revenues																	43,911	81,988	3,621
Cost and expense items:
General and administrative																	194	122	216
Interest expense																	489	591	601
Foreign exchange (gains) losses on non-U.S. Dollar denominated debt																	970	(193)	(366)
Income tax expense (benefit)																	(263)	51	(851)
Total costs and expenses																	1,390	571	(400)
Net earnings attributable to Berkshire Hathaway shareholders																	42,521	81,417	4,021
Other comprehensive income, net																	1,000	(228)	(2,211)
Comprehensive income attributable to Berkshire Hathaway shareholders																	$ 43,521	$ 81,189	$ 1,810

[1] * Includes after-tax investment and derivative gains/losses as follows:       1^st Quarter     2^nd Quarter     3^rd Quarter     4^th Quarter   2020   $ (55,617 )   $ 31,645     $ 24,737     $ 30,826   2019     16,106       7,934       8,666       24,739