Reconciliation of Expected Income Tax Expense at Federal Statutory Rate of 35% to Company's Applicable Income Tax Expense (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Tax at statutory rate	$ 709	$ 610	$ 2,030	$ 1,671
State income tax, at statutory rates, net of federal tax benefit	53	53	157	114
Tax effect of
Tax credits, net of related expenses	(120)	(124)	(322)	(319)
Tax-exempt income	(55)	(57)	(165)	(170)
Noncontrolling interests	15	8	39	22
Other items	(9)		(55)	(4)
Applicable income taxes	$ 593	$ 490	$ 1,684	$ 1,314

The sum of the current income tax expense or benefit and the deferred income tax expense or benefit pertaining to continuing operations.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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

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The amount of income tax expense or benefit for the period computed by applying the domestic federal statutory tax rates to pretax income from continuing operations.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef

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The portion of the difference between total income tax expense or benefit as reported in the Income Statement for the period and the expected income tax expense or benefit computed by applying the domestic federal statutory income tax rates to pretax income from continuing operations attributable to noncontrolling interest income or expense that is exempt from income taxes under enacted tax laws.

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The sum of the differences between total income tax expense or benefit as reported in the Income Statement for the period and the expected income tax expense or benefit computed by applying the domestic federal statutory income tax rates to pretax income from continuing operations attributable to tax credits.

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