Investments in equity securities (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014		Dec. 31, 2013
Summary of Investment Holdings [Line Items]
Fair value of investments	$ 118,486		$ 117,505
Equity Securities [Member]
Summary of Investment Holdings [Line Items]
Cost basis of investments	60,188		59,451
Unrealized gains on investments	58,582		58,197
Unrealized losses on investments	(284)		(143)
Fair value of investments	118,486	[1]	117,505	[2]
Banks, insurance and finance [Member] | Equity Securities [Member]
Summary of Investment Holdings [Line Items]
Cost basis of investments	22,410		22,420
Unrealized gains on investments	30,042		28,021
Unrealized losses on investments	(7)
Fair value of investments	52,445		50,441
Consumer products [Member] | Equity Securities [Member]
Summary of Investment Holdings [Line Items]
Cost basis of investments	7,083		7,082
Unrealized gains on investments	16,652		17,854
Unrealized losses on investments	(1)
Fair value of investments	23,734		24,936
Commercial, industrial and other [Member] | Equity Securities [Member]
Summary of Investment Holdings [Line Items]
Cost basis of investments	30,695		29,949
Unrealized gains on investments	11,888		12,322
Unrealized losses on investments	(276)		(143)
Fair value of investments	$ 42,307		$ 42,128

[1] As of March 31, 2014, approximately 56% of the aggregate fair value was concentrated in the equity securities of four companies (American Express Company - $13.6 billion; Wells Fargo & Company - $24.0 billion; International Business Machines Corporation - $13.2 billion; and The Coca-Cola Company - $15.5 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).