Investments in equity securities (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Summary of Investment Holdings [Line Items]
Cost Basis of Investments	$ 51,075	$ 50,507
Unrealized Gains on Investments	46,210	37,357
Unrealized Losses on Investments	(122)	(202)
Fair Value of Investments	97,163	87,662
Banks, insurance and finance [Member]
Summary of Investment Holdings [Line Items]
Cost Basis of Investments	19,360	18,600
Unrealized Gains on Investments	18,216	14,753
Unrealized Losses on Investments		(2)
Fair Value of Investments	37,576	33,351
Consumer products [Member]
Summary of Investment Holdings [Line Items]
Cost Basis of Investments	7,374	7,546
Unrealized Gains on Investments	17,458	14,917
Fair Value of Investments	24,832	22,463
Commercial, industrial and other [Member]
Summary of Investment Holdings [Line Items]
Cost Basis of Investments	24,341	24,361
Unrealized Gains on Investments	10,536	7,687
Unrealized Losses on Investments	(122)	(200)
Fair Value of Investments	$ 34,755	$ 31,848

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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