Condensed Financial Information - Statements of Cash Flows (Detail) - USD ($) $ in Millions	3 Months Ended																12 Months Ended
	Dec. 31, 2020		Sep. 30, 2020	[1]	Jun. 30, 2020	[1]	Mar. 31, 2020		Dec. 31, 2019		Sep. 30, 2019	[1]	Jun. 30, 2019	[1]	Mar. 31, 2019		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities:
Net earnings attributable to Berkshire Hathaway shareholders	$ 35,835	[1]	$ 30,137		$ 26,295		$ (49,746)	[1]	$ 29,159	[1]	$ 16,524		$ 14,073		$ 21,661	[1]	$ 42,521	$ 81,417	$ 4,021
Adjustments to reconcile net earnings to cash flows from operating activities:
Investment gains/losses																	(40,905)	(71,123)	22,155
Income taxes payable																	7,195	15,181	(4,957)
Net cash flows from operating activities																	39,773	38,687	37,400
Cash flows from investing activities:
Other																	(3,582)	(1,496)	(71)
Net cash flows from investing activities																	(37,757)	(5,621)	(32,849)
Cash flows from financing activities:
Acquisition of treasury stock																	(24,706)	(4,850)	(1,346)
Other																	(429)	(497)	(343)
Net cash flows from financing activities																	(18,344)	730	(5,812)
Other cash flow information:
Income taxes paid																	5,001	5,415	4,354
Berkshire Hathaway Inc. (Parent) [Member]
Cash flows from operating activities:
Net earnings attributable to Berkshire Hathaway shareholders																	42,521	81,417	4,021
Adjustments to reconcile net earnings to cash flows from operating activities:
Investment gains/losses																	24	125	4
Undistributed earnings of consolidated subsidiaries																	(17,402)	(65,237)	3,952
Non-cash dividends from subsidiaries																	(8,296)
Income taxes payable																	(72)	(56)	(972)
Other																	1,100	(693)	3,062
Net cash flows from operating activities																	17,875	15,556	10,067
Cash flows from investing activities:
Investments in and advances to/from consolidated subsidiaries, net																	(1,947)	60	460
Purchases of U.S. Treasury Bills																	(54,715)	(40,107)	(29,740)
Sales and maturities of U.S. Treasury Bills																	59,035	36,943	21,442
Other																	11	737
Net cash flows from investing activities																	2,384	(2,367)	(7,838)
Cash flows from financing activities:
Proceeds from borrowings																	2,923	3,967	17
Repayments of borrowings																	(1,151)	(758)	(1,563)
Acquisition of treasury stock																	(24,706)	(4,850)	(1,346)
Other																		19	61
Net cash flows from financing activities																	(22,934)	(1,622)	(2,831)
Increase (decrease) in cash and cash equivalents																	(2,675)	11,567	(602)
Cash and cash equivalents at beginning of year							$ 15,004								$ 3,437		15,004	3,437	4,039
Cash and cash equivalents at end of year	$ 12,329								$ 15,004								12,329	15,004	3,437
Other cash flow information:
Income taxes paid																	3,391	3,531	2,790
Interest paid																	$ 359	$ 364	$ 388

[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