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Valuation Accounts (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Supplemental Financial Information [Line Items]
Accumulated depreciation	$ 18,777	$ 18,591
Allowance for doubtful accounts	$ 118	$ 126

- Definition

The cumulative amount of depreciation, depletion and amortization (related to property, plant and equipment, but not including land) that has been recognized in the income statement.

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