Income Taxes (Details) (USD $) In Millions	3 Months Ended
Jun. 30, 2011	Jun. 30, 2012
Income Taxes (Textuals)
Unrecognized tax benefits expense	$ 642
Unrecognized tax benefits that would impact income tax expense and the effective tax rate	421
Potential reduction of unrecognized benefits due to audit resolutions and expiration of statutes of limitations		156
Accrued interest on unrecognized tax benefits	138
Income tax expense, before any tax effect, related to interest	3
Canada Revenue Agency Assessments [Member]
Income Tax Contingency [Line Items]
Transfer pricing related to Canada Revenue Agency for 2003 through 2007	169
Internal Revenue Service Agency Assessments [Member]
Income Tax Contingency [Line Items]
Tax assessments as per revenue agent reports for 2003 through 2006	$ 98

Income Taxes.

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Tax assessments as per revenue agent reports.

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The amount of estimated interest recognized in the period arising from income tax examinations.

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The amount of the unrecognized tax benefit of a position taken for which it is reasonably possible that the total amount thereof will significantly increase or decrease within twelve months of the balance sheet date.

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Reflects the effects of adjustments of previously recorded tax expense, significant settlements of income tax disputes, and unusual tax positions or infrequent actions taken by the entity, including tax assessment reversal, IRS tax settlement and unusual repatriation of foreign earnings.

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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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This element represents the amount of interest expense accrued as of the date of the statement of financial position for an underpayment of income taxes computed by applying the applicable statutory rate of interest to the difference between a tax position recognized for financial reporting purposes and the amount previously taken or expected to be taken in a tax return of the entity.

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The total amount of unrecognized tax benefits that, if recognized, would affect the effective tax rate.

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