Investments in equity securities (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Summary of Investment Holdings [Line Items]
Cost Basis of Investments	$ 50,507	$ 49,610
Unrealized Gains on Investments	37,357	28,773
Unrealized Losses on Investments	(202)	(1,392)
Fair Value of Investments	87,662	76,991
Banks, insurance and finance [Member]
Summary of Investment Holdings [Line Items]
Cost Basis of Investments	18,600	16,697
Unrealized Gains on Investments	14,753	9,480
Unrealized Losses on Investments	(2)	(1,269)
Fair Value of Investments	33,351	24,908
Consumer products [Member]
Summary of Investment Holdings [Line Items]
Cost Basis of Investments	7,546	12,390
Unrealized Gains on Investments	14,917	14,320
Fair Value of Investments	22,463	26,710
Commercial, industrial and other [Member]
Summary of Investment Holdings [Line Items]
Cost Basis of Investments	24,361	20,523
Unrealized Gains on Investments	7,687	4,973
Unrealized Losses on Investments	(200)	(123)
Fair Value of Investments	$ 31,848	$ 25,373

Amount of equity securities categorized neither as held-to-maturity nor as trading.

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Reference 2: http://www.xbrl.org/2003/role/presentationRef

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Reference 3: http://www.xbrl.org/2003/role/presentationRef

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 4: http://www.xbrl.org/2003/role/presentationRef

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Reference 5: http://www.xbrl.org/2003/role/presentationRef

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Reference 9: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 10: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

- Definition

This item represents the gross unrealized gains for securities, at a point in time, which are categorized neither as held-to-maturity nor trading securities.

+ References+ Details