Investments in equity securities (Detail) - USD ($) $ in Millions	Mar. 31, 2017		Dec. 31, 2016
Summary of Investment Holdings [Line Items]
Cost basis of investments	$ 72,458		$ 66,377
Unrealized gains on investments	62,718		56,365
Unrealized losses on investments	(156)		(710)
Fair value of investments	135,020	[1]	122,032	[2]
Banks, insurance and finance [Member]
Summary of Investment Holdings [Line Items]
Cost basis of investments	20,431		19,852
Unrealized gains on investments	31,725		30,572
Fair value of investments	52,156		50,424
Consumer products [Member]
Summary of Investment Holdings [Line Items]
Cost basis of investments	19,320		10,657
Unrealized gains on investments	21,020		16,760
Unrealized losses on investments			(9)
Fair value of investments	40,340		27,408
Commercial, industrial and other [Member]
Summary of Investment Holdings [Line Items]
Cost basis of investments	32,707		35,868
Unrealized gains on investments	9,973		9,033
Unrealized losses on investments	(156)		(701)
Fair value of investments	$ 42,524		$ 44,200

[1] Approximately 65% of the aggregate fair value was concentrated in the equity securities of five companies: American Express Company - $12.0 billion, Apple Inc. - $19.2 billion, The Coca-Cola Company - $17.0 billion, International Business Machines Corporation ("IBM") - $11.2 billion and Wells Fargo & Company - $27.8 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, IBM - $13.5 billion and Wells Fargo & Company - $27.6 billion.