Significant business acquisitions - Estimated fair values of assets acquired and liabilities assumed (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Feb. 29, 2016	Jan. 29, 2016	Dec. 31, 2015
Business Acquisition [Line Items]
Goodwill	$ 81,258	$ 79,486			$ 62,708
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