Investments in equity securities (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014		Dec. 31, 2013
Summary of Investment Holdings [Line Items]
Cost basis of investments	$ 60,645		$ 59,451
Unrealized gains on investments	58,446		58,197
Unrealized losses on investments	(182)		(143)
Fair value of investments	118,909	[1]	117,505	[2]
Banks, insurance and finance [Member]
Summary of Investment Holdings [Line Items]
Cost basis of investments	22,468		22,420
Unrealized gains on investments	30,226		28,021
Unrealized losses on investments	(2)
Fair value of investments	52,692		50,441
Consumer products [Member]
Summary of Investment Holdings [Line Items]
Cost basis of investments	7,005		7,082
Unrealized gains on investments	18,620		17,854
Unrealized losses on investments	(4)
Fair value of investments	25,621		24,936
Commercial, industrial and other [Member]
Summary of Investment Holdings [Line Items]
Cost basis of investments	31,172		29,949
Unrealized gains on investments	9,600		12,322
Unrealized losses on investments	(176)		(143)
Fair value of investments	$ 40,596		$ 42,128

[1] As of September 30, 2014, approximately 58% of the aggregate fair value was concentrated in the equity securities of four companies (American Express Company - $13.3 billion; Wells Fargo & Company - $25.1 billion; International Business Machines Corporation - $13.4 billion; and The Coca-Cola Company - $17.1 billion).

[2] As of December 31, 2013, approximately 55% of the aggregate fair value was concentrated in the equity securities of four companies (American Express Company - $13.8 billion; Wells Fargo & Company - $21.9 billion; International Business Machines Corporation - $12.8 billion; and The Coca-Cola Company - $16.5 billion).