Significant business acquisitions - Estimated fair values of assets acquired and liabilities assumed (Detail) - USD ($)
$ in Millions
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Feb. 29, 2016
Jan. 29, 2016
Business Acquisition [Line Items]          
Goodwill $ 81,025 $ 81,258 $ 79,486    
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