Quarterly data (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended																12 Months Ended
	Dec. 31, 2012		Sep. 30, 2012		Jun. 30, 2012		Mar. 31, 2012		Dec. 31, 2011		Sep. 30, 2011		Jun. 30, 2011		Mar. 31, 2011		Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Quarterly Financial Information [Line Items]
Revenues	$ 44,720		$ 41,050		$ 38,546		$ 38,147		$ 37,955		$ 33,739		$ 38,274		$ 33,720		$ 162,463	$ 143,688	$ 136,185
Net earnings attributable to Berkshire Hathaway	4,551	[1]	3,920	[1]	3,108	[1]	3,245	[1]	3,048	[1]	2,278	[1]	3,417	[1]	1,511	[1]	14,824	10,254	12,967
Net earnings attributable to Berkshire per equivalent Class A common share	$ 2,757		$ 2,373		$ 1,882		$ 1,966		$ 1,846		$ 1,380		$ 2,072		$ 917
Investment and derivative gains/losses	$ 1,738		$ 521		$ (612)		$ 580		$ 382		$ (1,534)		$ 713		$ (82)

[1] Includes realized investment gains/losses, other-than-temporary impairment losses on investments and derivative gains/losses. Derivative gains/losses include significant amounts related to non-cash changes in the fair value of long-term contracts arising from short-term changes in equity prices, interest rates and foreign currency rates, among other factors. After-tax investment and derivative gains/losses for the periods presented above are as follows (in millions): 1st Quarter 2nd Quarter 3rd Quarter 4th Quarter Investment and derivative gains/losses - 2012 $ 580 $ (612 ) $ 521 $ 1,738 Investment and derivative gains/losses - 2011 (82 ) 713 (1,534 ) 382