Investments in equity securities - fair value by segment (Detail) (USD $) In Millions	Sep. 30, 2011		Dec. 31, 2010
Investments in equity securities [Line Items]
Fair Value	$ 68,062		$ 61,513
Insurance and Other [Member]
Investments in equity securities [Line Items]
Fair Value	67,225		59,819
Railroad, Utilities and Energy [Member]
Investments in equity securities [Line Items]
Fair Value	381	[1]	1,182	[1]
Finance and Financial Products [Member]
Investments in equity securities [Line Items]
Fair Value	$ 456	[1]	$ 512	[1]

[1] Included in Other assets.