Investments in equity securities (Detail) - USD ($) $ in Millions	Sep. 30, 2017		Dec. 31, 2016
Summary of Investment Holdings [Line Items]
Cost basis of investments	$ 76,179		$ 66,377
Unrealized gains on investments	82,218		56,365
Unrealized losses on investments	(747)		(710)
Fair value of investments	157,650	[1]	122,032	[2]
Banks, insurance and finance [Member]
Summary of Investment Holdings [Line Items]
Cost basis of investments	26,792		19,852
Unrealized gains on investments	45,910		30,572
Fair value of investments	72,702		50,424
Consumer products [Member]
Summary of Investment Holdings [Line Items]
Cost basis of investments	20,097		10,657
Unrealized gains on investments	23,910		16,760
Unrealized losses on investments			(9)
Fair value of investments	44,007		27,408
Commercial, industrial and other [Member]
Summary of Investment Holdings [Line Items]
Cost basis of investments	29,290		35,868
Unrealized gains on investments	12,398		9,033
Unrealized losses on investments	(747)		(701)
Fair value of investments	$ 40,941		$ 44,200

[1] Approximately 62% of the aggregate fair value was concentrated in the equity securities of five companies: American Express Company - $13.7 billion, Apple Inc. - $21.3 billion, Bank of America Corporation - $17.7 billion, The Coca-Cola Company - $18.0 billion and Wells Fargo & Company - $26.9 billion.

[2] Approximately 62% of the aggregate fair value was concentrated in the equity securities of five companies: American Express Company - $11.2 billion, Apple Inc. - $7.1 billion, The Coca-Cola Company - $16.6 billion, International Business Machines Corporation - $13.5 billion and Wells Fargo & Company - $27.6 billion.