Summary of Activity Related to Gross Unrecognized Tax Benefits (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Beginning Balance	$ 1,564	$ 1,140	$ 1,188
Increases related to prior year tax positions	43	77	37
Decreases related to prior year tax positions	(40)	(9)	(197)
Decreases related to settlement with tax authorities	(62)	(5)	(47)
Decreases as a result of a lapse of applicable statute of limitation			(97)
Increases related to acquisition	17
Increases related to current year tax positions	411	361	256
Ending Balance	$ 1,933	$ 1,564	$ 1,140

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The gross amount of unrecognized tax benefits pertaining to uncertain tax positions taken in tax returns as of the balance sheet date.

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The gross amount of decreases in unrecognized tax benefits resulting from tax positions taken in prior period tax returns, excluding amounts pertaining to examined tax returns.

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The gross amount of decreases in unrecognized tax benefits resulting from settlements with taxing authorities.

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Gross amount of increases in unrecognized tax benefits resulting from acquisitions.

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