Condensed Financial Information - Statements of Cash Flows (Detail) - USD ($) $ in Millions	3 Months Ended																12 Months Ended
	Dec. 31, 2019		Sep. 30, 2019	[1]	Jun. 30, 2019	[1]	Mar. 31, 2019		Dec. 31, 2018		Sep. 30, 2018	[1]	Jun. 30, 2018	[1]	Mar. 31, 2018		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash flows from operating activities:
Net earnings attributable to Berkshire Hathaway shareholders	$ 29,159	[1]	$ 16,524		$ 14,073		$ 21,661	[1]	$ (25,392)	[1]	$ 18,540		$ 12,011		$ (1,138)	[1]	$ 81,417	$ 4,021	$ 44,940
Adjustments to reconcile net earnings to cash flows from operating activities:
Investment gains/losses																	(71,123)	22,155	(1,410)
Income taxes payable																	15,181	(4,957)	(24,957)
Other																	(1,254)	2,957	458
Net cash flows from operating activities																	38,687	37,400	45,728
Cash flows from investing activities:
Other																	(1,496)	(71)	(3,608)
Net cash flows from investing activities																	(5,621)	(32,849)	(41,009)
Cash flows from financing activities:
Acquisition of treasury stock																	(4,850)	(1,346)
Other																	(497)	(343)	(121)
Net cash flows from financing activities																	730	(5,812)	(1,398)
Other cash flow information:
Income taxes paid																	5,415	4,354	3,286
Berkshire Hathaway Inc. (Parent) [Member]
Cash flows from operating activities:
Net earnings attributable to Berkshire Hathaway shareholders																	81,417	4,021	44,940
Adjustments to reconcile net earnings to cash flows from operating activities:
Investment gains/losses																	125	4	1
Undistributed earnings of consolidated subsidiaries																	(65,237)	3,952	(37,832)
Income taxes payable																	(56)	(972)	(135)
Other																	(693)	3,062	(1,234)
Net cash flows from operating activities																	15,556	10,067	5,740
Cash flows from investing activities:
Investments in and advances to/from consolidated subsidiaries, net																	60	460	(239)
Purchases of U.S. Treasury Bills																	(40,107)	(29,740)	(19,663)
Sales and maturities of U.S. Treasury Bills																	36,943	21,442	14,847
Other																	737
Net cash flows from investing activities																	(2,367)	(7,838)	(5,055)
Cash flows from financing activities:
Proceeds from borrowings																	3,967	17	1,201
Repayments of borrowings																	(758)	(1,563)	(1,145)
Acquisition of treasury stock																	(4,850)	(1,346)
Other																	19	61	77
Net cash flows from financing activities																	(1,622)	(2,831)	133
Increase (decrease) in cash and cash equivalents																	11,567	(602)	818
Cash and cash equivalents at beginning of year							$ 3,437								$ 4,039		3,437	4,039	3,221
Cash and cash equivalents at end of year	$ 15,004								$ 3,437								15,004	3,437	4,039
Other cash flow information:
Income taxes paid																	3,531	2,790	2,076
Interest paid																	$ 364	$ 388	$ 386

[1] * Includes after-tax investment and derivative gains/losses as follows:       1^st Quarter     2^nd Quarter     3^rd Quarter     4^th Quarter   2019   $ 16,106     $ 7,934     $ 8,666     $ 24,739   2018     (6,426 )     5,118       11,660       (28,089 )