Investments in equity securities (Detail) - USD ($) $ in Millions	Sep. 30, 2015		Dec. 31, 2014
Summary of Investment Holdings [Line Items]
Cost basis of investments	$ 63,047		$ 58,370
Unrealized gains on investments	50,221		60,137
Unrealized losses on investments	(2,980)		(1,037)
Fair value of investments	110,288	[1]	117,470	[2]
Banks, insurance and finance [Member]
Summary of Investment Holdings [Line Items]
Cost basis of investments	21,587		22,495
Unrealized gains on investments	27,358		33,170
Unrealized losses on investments	(86)
Fair value of investments	48,859		55,665
Consumer products [Member]
Summary of Investment Holdings [Line Items]
Cost basis of investments	6,893		6,951
Unrealized gains on investments	16,620		18,389
Unrealized losses on investments	(5)		(1)
Fair value of investments	23,508		25,339
Commercial, industrial and other [Member]
Summary of Investment Holdings [Line Items]
Cost basis of investments	34,567		28,924
Unrealized gains on investments	6,243		8,578
Unrealized losses on investments	(2,889)		(1,036)
Fair value of investments	$ 37,921		$ 36,466

[1] Approximately 58% of the aggregate fair value was concentrated in the equity securities of four companies (American Express Company - $11.2 billion; Wells Fargo & Company - $25.2 billion; International Business Machines Corporation ("IBM") - $11.7 billion; and The Coca-Cola Company - $16.0 billion).

[2] Approximately 59% of the aggregate fair value was concentrated in the equity securities of four companies (American Express Company - $14.1 billion; Wells Fargo & Company - $26.5 billion; International Business Machines Corporation ("IBM") - $12.3 billion; and The Coca-Cola Company - $16.9 billion).