Investments in equity securities (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Summary of Investment Holdings [Line Items]
Cost Basis of Investments	$ 55,803	$ 50,507
Unrealized Gains on Investments	47,808	37,357
Unrealized Losses on Investments	(337)	(202)
Fair Value of Investments	103,274	87,662
Banks, insurance and finance [Member]
Summary of Investment Holdings [Line Items]
Cost Basis of Investments	20,259	18,600
Unrealized Gains on Investments	21,600	14,753
Unrealized Losses on Investments		(2)
Fair Value of Investments	41,859	33,351
Consumer products [Member]
Summary of Investment Holdings [Line Items]
Cost Basis of Investments	7,272	7,546
Unrealized Gains on Investments	17,178	14,917
Fair Value of Investments	24,450	22,463
Commercial, industrial and other [Member]
Summary of Investment Holdings [Line Items]
Cost Basis of Investments	28,272	24,361
Unrealized Gains on Investments	9,030	7,687
Unrealized Losses on Investments	(337)	(200)
Fair Value of Investments	$ 36,965	$ 31,848