Significant business acquisitions - Estimated fair values of assets acquired and liabilities assumed (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Feb. 29, 2016	Jan. 29, 2016	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2014	Dec. 01, 2014
Business Acquisition [Line Items]
Goodwill	$ 79,486			$ 62,708		$ 60,714
Precision Castparts Corp. [Member]
Business Acquisition [Line Items]
Cash and cash equivalents			$ 250
Inventories			3,430
Property, plant and equipment			2,765
Goodwill			16,011
Other intangible assets			23,527
Other assets			1,916
Assets acquired			47,899
Accounts payable, accruals and other liabilities			2,442
Notes payable and other borrowings			5,251
Income taxes, principally deferred			7,548
Liabilities assumed			15,241
Net assets			$ 32,658
Duracell Company [Member]
Business Acquisition [Line Items]
Cash and cash equivalents		$ 1,807
Inventories		319
Property, plant and equipment		359
Goodwill		866
Other intangible assets		1,550
Other assets		242
Assets acquired		5,143
Accounts payable, accruals and other liabilities		410
Income taxes, principally deferred		494
Liabilities assumed		904
Net assets		$ 4,239
Berkshire Hathaway Automotive (previously Van Tuyl Group) [Member]
Business Acquisition [Line Items]
Cash and investments					$ 1,274
Property, plant and equipment					1,045
Goodwill					1,833
Other assets					2,488
Assets acquired					6,640
Accounts payable, accruals and other liabilities					1,399
Notes payable and other borrowings					1,129
Liabilities assumed					2,528
Net assets					$ 4,112
AltaLink [Member]
Business Acquisition [Line Items]
Cash and investments							$ 15
Property, plant and equipment							5,610
Goodwill							1,744
Other assets							300
Assets acquired							7,669
Accounts payable, accruals and other liabilities							1,090
Notes payable and other borrowings							3,851
Liabilities assumed							4,941
Net assets							$ 2,728