Condensed Financial Information - Statements of Cash Flows (Detail) - USD ($) $ in Millions	3 Months Ended																12 Months Ended
	Dec. 31, 2017		Sep. 30, 2017	[1]	Jun. 30, 2017	[1]	Mar. 31, 2017		Dec. 31, 2016		Sep. 30, 2016	[1]	Jun. 30, 2016	[1]	Mar. 31, 2016		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities:
Net earnings attributable to Berkshire Hathaway shareholders	$ 32,551	[1]	$ 4,067		$ 4,262		$ 4,060	[1]	$ 6,286	[1]	$ 7,198		$ 5,001		$ 5,589	[1]	$ 44,940	$ 24,074	$ 24,083
Adjustments to reconcile net earnings to cash flows from operating activities:
Investment gains/losses																	(1,410)	(7,553)	(9,373)
Income taxes payable																	(24,957)	4,044	5,718
Other																	458	(161)	751
Net cash flows from operating activities																	45,776	32,535	31,491
Cash flows from investing activities:
Purchases of U.S. Treasury Bills and fixed maturity securities																	(158,492)	(96,568)	(17,891)
Net cash flows from investing activities																	(41,091)	(84,267)	(28,001)
Cash flows from financing activities:
Other																	(121)	112	(233)
Net cash flows from financing activities																	(1,398)	12,791	3,803
Increase (decrease) in cash and cash equivalents																	3,535	(39,113)	7,128
Cash and cash equivalents at beginning of year							28,048								67,161		28,048	67,161	60,033
Cash and cash equivalents at end of year	31,583								28,048								31,583	28,048	67,161
Other cash flow information:
Income taxes paid																	3,286	4,719	4,535
U.S. Treasury Bills [Member]
Cash flows from financing activities:
Cash and cash equivalents at end of year	5,700																5,700
Berkshire Hathaway Inc. (Parent) [Member]
Cash flows from operating activities:
Net earnings attributable to Berkshire Hathaway shareholders																	44,940	24,074	24,083
Adjustments to reconcile net earnings to cash flows from operating activities:
Investment gains/losses																	1	(700)	(6,854)
Undistributed earnings of consolidated subsidiaries																	(37,832)	(13,264)	(8,508)
Non-cash dividends from consolidated subsidiaries																			(3,938)
Income taxes payable																	(135)	629	2,227
Other																	(1,234)	(161)	222
Net cash flows from operating activities																	5,740	10,578	7,232
Cash flows from investing activities:
Redemption (purchase) of Kraft Heinz Company investments																		8,320	(5,258)
Investments in and advances to/repayments from consolidated subsidiaries, net																	(239)	(26,398)	(2,274)
Net cash flows from investing activities																	(5,055)	(26,283)	(7,532)
Cash flows from financing activities:
Proceeds from borrowings																	1,201	9,278	3,165
Repayments of borrowings																	(1,145)	(1,125)	(1,775)
Other																	77	164	70
Net cash flows from financing activities																	133	8,317	1,460
Increase (decrease) in cash and cash equivalents																	818	(7,388)	1,160
Cash and cash equivalents at beginning of year							$ 3,221								$ 10,609		3,221	10,609	9,449
Cash and cash equivalents at end of year	$ 4,039								$ 3,221								4,039	3,221	10,609
Other cash flow information:
Income taxes paid																	2,076	3,583	3,180
Interest paid																	386	307	206
Non-cash investments in consolidated subsidiaries																			$ 3,938
Berkshire Hathaway Inc. (Parent) [Member] | U.S. Treasury Bills [Member]
Cash flows from investing activities:
Purchases of U.S. Treasury Bills and fixed maturity securities																	(19,663)	(9,350)
Sales and maturities of U.S. Treasury Bills																	$ 14,847	$ 1,145

[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 - 2017 $ 504 $ 143 $ 623 $ 107 Investment and derivative gains/losses - 2016 1,852 394 2,347 1,904 Income tax net benefit - Tax Cuts and Jobs Act of 2017 - - - 28,200