Accumulated other comprehensive income - Rollforward (Detail) (USD $) In Millions, unless otherwise specified			9 Months Ended
Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2013 Portion Attributable to Berkshire Hathaway Shareholders [Member]	Sep. 30, 2013 Unrealized appreciation of investments, net [Member] Portion Attributable to Berkshire Hathaway Shareholders [Member]	Sep. 30, 2013 Foreign currency translation [Member] Portion Attributable to Berkshire Hathaway Shareholders [Member]	Sep. 30, 2013 Prior service and actuarial gains/losses of defined benefit pension plans [Member] Portion Attributable to Berkshire Hathaway Shareholders [Member]	Sep. 30, 2013 Other AOCI transactions [Member] Portion Attributable to Berkshire Hathaway Shareholders [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ 34,897	$ 27,500	$ 27,500	$ 29,254	$ (120)	$ (1,601)	$ (33)
Other comprehensive income (loss) before reclassifications			8,093	8,252	(191)	(17)	49
Amounts reclassified from accumulated other comprehensive income			(684)	(738)	(31)	81	4
Transactions with noncontrolling interests			(12)		(12)
Net changes in current period			7,397	7,514	(234)	64	53
Ending Balance	$ 34,897	$ 27,500	$ 34,897	$ 36,768	$ (354)	$ (1,537)	$ 20

- Definition

Accumulated change in equity from transactions and other events and circumstances from non-owner sources, net of tax effect, at period end. Excludes Net Income (Loss), and accumulated changes in equity from transactions resulting from investments by owners and distributions to owners. Includes foreign currency translation items, certain pension adjustments, unrealized gains and losses on certain investments in debt and equity securities, other than temporary impairment (OTTI) losses related to factors other than credit losses on available-for-sale and held-to-maturity debt securities that an entity does not intend to sell and it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis, as well as changes in the fair value of derivatives related to the effective portion of a designated cash flow hedge.

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