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Supplemental Financial Statement Information (Valuation Accounts) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Supplemental Financial Statement Information [Abstract]
Accumulated depreciation	$ 18,691	$ 18,591
Allowance for doubtful accounts	$ 133	$ 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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