Condensed Financial Information - Statements of Cash Flows (Detail) - USD ($) $ in Millions	3 Months Ended																12 Months Ended
	Dec. 31, 2018		Sep. 30, 2018	[1]	Jun. 30, 2018	[1]	Mar. 31, 2018		Dec. 31, 2017		Sep. 30, 2017	[1]	Jun. 30, 2017	[1]	Mar. 31, 2017		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash flows from operating activities:
Net earnings attributable to Berkshire Hathaway shareholders	$ (25,392)	[1]	$ 18,540		$ 12,011		$ (1,138)	[1]	$ 32,551	[1]	$ 4,067		$ 4,262		$ 4,060	[1]	$ 4,021	$ 44,940	$ 24,074
Adjustments to reconcile net earnings to cash flows from operating activities:
Investment gains (losses)																	22,155	(1,410)	(7,553)
Income taxes payable																	(4,957)	(24,957)	4,044
Other																	2,957	458	(161)
Net cash flows from operating activities																	37,400	45,728	32,647
Cash flows from investing activities:
Net cash flows from investing activities																	(32,849)	(41,009)	(84,225)
Cash flows from financing activities:
Acquisition of treasury stock																	(1,346)
Other																	(343)	(121)	112
Net cash flows from financing activities																	(5,812)	(1,398)	12,791
Other cash flow information:
Income taxes paid																	4,354	3,286	4,719
Berkshire Hathaway Inc. (Parent) [Member]
Cash flows from operating activities:
Net earnings attributable to Berkshire Hathaway shareholders																	4,021	44,940	24,074
Adjustments to reconcile net earnings to cash flows from operating activities:
Investment gains (losses)																	4	1	(700)
Undistributed earnings of consolidated subsidiaries																	3,952	(37,832)	(13,264)
Income taxes payable																	(972)	(135)	629
Other																	3,062	(1,234)	(161)
Net cash flows from operating activities																	10,067	5,740	10,578
Cash flows from investing activities:
Redemption of Kraft Heinz Company preferred stock																			8,320
Investments in and advances to/from consolidated subsidiaries, net																	460	(239)	(26,398)
Purchases of U.S. Treasury Bills																	(29,740)	(19,663)	(9,350)
Sales and maturities of U.S. Treasury Bills																	21,442	14,847	1,145
Net cash flows from investing activities																	(7,838)	(5,055)	(26,283)
Cash flows from financing activities:
Proceeds from borrowings																	17	1,201	9,278
Repayments of borrowings																	(1,563)	(1,145)	(1,125)
Acquisition of treasury stock																	(1,346)
Other																	61	77	164
Net cash flows from financing activities																	(2,831)	133	8,317
Increase (decrease) in cash and cash equivalents																	(602)	818	(7,388)
Cash and cash equivalents at beginning of year							$ 4,039								$ 3,221		4,039	3,221	10,609
Cash and cash equivalents at end of year	$ 3,437								$ 4,039								3,437	4,039	3,221
Other cash flow information:
Income taxes paid																	2,790	2,076	3,583
Interest paid																	$ 388	$ 386	$ 307

[1] Includes after-tax investment and derivative gains/losses and a one-time income tax net benefit attributable to the enactment of the Tax Cuts and Jobs Act of 2017 as follows: 1st Quarter 2nd Quarter 3rd Quarter 4th Quarter Investment and derivative gains/losses - 2018 $ (6,426) $ 5,118 $ 11,660 $ (28,089) Investment and derivative gains/losses - 2017 504 143 623 107 Income tax net benefit - Tax Cuts and Jobs Act of 2017 - - - 28,200