Significant business acquisitions - Estimated fair values of assets acquired and liabilities assumed (Detail) - USD ($) $ in Millions	Sep. 30, 2016	Feb. 29, 2016	Jan. 29, 2016	Dec. 31, 2015	Dec. 31, 2014
Business Acquisition [Line Items]
Goodwill	$ 79,392			$ 62,708	$ 60,714
Precision Castparts Corp. [Member]
Business Acquisition [Line Items]
Cash and cash equivalents			$ 250
Inventories			3,430
Property, plant and equipment			2,772
Goodwill			15,880
Other intangible assets			24,197
Other assets			1,914
Assets acquired			48,443
Accounts payable, accruals and other liabilities			2,442
Notes payable and other borrowings			5,251
Income taxes, principally deferred			8,092
Liabilities assumed			15,785
Net assets			$ 32,658
Duracell Company [Member]
Business Acquisition [Line Items]
Cash and cash equivalents		$ 1,807
Inventories		326
Property, plant and equipment		364
Goodwill		614
Other intangible assets		2,024
Other assets		256
Assets acquired		5,391
Accounts payable, accruals and other liabilities		392
Income taxes, principally deferred		760
Liabilities assumed		1,152
Net assets		$ 4,239