Investments in equity securities (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Summary of Investment Holdings [Line Items]
Cost Basis of Investments	$ 51,194	$ 49,610
Unrealized Gains on Investments	35,710	28,773
Unrealized Losses on Investments	(688)	(1,392)
Fair Value of Investments	86,216	76,991
Banks, insurance and finance [Member]
Summary of Investment Holdings [Line Items]
Cost Basis of Investments	17,661	16,697
Unrealized Gains on Investments	13,665	9,480
Unrealized Losses on Investments	(230)	(1,269)
Fair Value of Investments	31,096	24,908
Consumer products [Member]
Summary of Investment Holdings [Line Items]
Cost Basis of Investments	9,843	12,390
Unrealized Gains on Investments	15,549	14,320
Unrealized Losses on Investments	(2)
Fair Value of Investments	25,390	26,710
Commercial, industrial and other [Member]
Summary of Investment Holdings [Line Items]
Cost Basis of Investments	23,690	20,523
Unrealized Gains on Investments	6,496	4,973
Unrealized Losses on Investments	(456)	(123)
Fair Value of Investments	$ 29,730	$ 25,373