Investments (Details 8) (USD $) In Millions			3 Months Ended	6 Months Ended
Sep. 30, 2011	Dec. 31, 2010	Sep. 30, 2011 Purchased Credit Impaired (PCI) Securities	Sep. 30, 2011 Purchased Credit Impaired (PCI) Securities
Purchased Credit Impaired (PCI) Securities
Contractually required payments (principal and interest)			$ 10,824	$ 10,824
Cash flows expected to be collected			8,250	8,250
Recorded investment in acquired securities			5,562	5,562
Outstanding principal balance			7,755	7,755
Amortized cost			5,233	5,233
Fair value	263,038	232,883	4,894	4,894
Changes in activity for the accretable yield on PCI securities:
Balance, beginning of period			2,276
Newly purchased PCI securities			306	2,688
Accretion			(119)	(194)
Effect of changes in interest rate indices			(46)	(54)
Net reclassification from (to) non-accretable difference, including effects of prepayments			(93)	(116)
Balance, end of period			$ 2,324	$ 2,324

Change in the estimate of cash flows expected to be collected, which results in an increase or decrease in accretable yield, due to effect of changes in interest rate indices. This relates to a loan accounted for as an available-for-sale debt security, with evidence of deterioration of credit quality since origination that was acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable.

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Change in the estimate of cash flows expected to be collected, which results in an increase or decrease in accretable yield. This relates to a loan accounted for as an available-for-sale debt security, with evidence of deterioration of credit quality since origination that was acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable.

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The recorded investment of the securities at the acquisition date. This relates to securities accounted for as available-for-sale debt securities, with evidence of deterioration of credit quality since origination that were acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable.

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This represents the outstanding principal of securities oustanding at the reporting date.

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This item represents the cost of debt securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents Available-for-sale Securities which consist of all investments in certain debt and equity securities neither classified as trading or held-to-maturity securities. A debt security represents a creditor relationship with an enterprise. Debt securities include, among other items, US Treasury securities, US government securities, municipal securities, corporate bonds, convertible debt, commercial paper, and all securitized debt instruments. An equity security represents an ownership interest in an enterprise or the right to acquire or dispose of an ownership interest in an enterprise at fixed or determinable prices. Equity securities include, among other things, common stock, certain preferred stock, warrant rights, call options, and put options, but do not include convertible debt. An entity may opt to provide the reader with additional narrative text to better understand the nature of investments in debt and equity securities which are categorized as Available-for-sale.

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-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 12

-Subparagraph b

-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 aggregate excess of a loan's cash flows expected to be collected over the investor's initial investment in the loan. This relates to loans accounted for as available-for-sale debt securities, with evidence of deterioration of credit quality since origination that were acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable.

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-Publisher AICPA

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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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Current period recognition of the accretion of the excess of a loan's cash flows expected to be collected over the investor's initial investment in the loan. This element relates to loans accounted for as available-for-sale debt securities, with evidence of deterioration of credit quality since origination that were acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable.

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Increases in the aggregate excess of a loan's cash flows expected to be collected over the investor's initial investment in the loan. This relates to loans accounted for as available-for-sale debt securities, with evidence of deterioration of credit quality since origination that were acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable.

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The investor's estimate, at acquisition, of the amount and timing of undiscounted principal, interest, and other cash flows expected to be collected. This would be the investor's best estimate of cash flows, including the effect of prepayments if considered, that is used in determining the acquisition price, and, in a business combination, the investor's estimate of fair value for purposes of acquisition price allocation. This relates to loans accounted for as available-for-sale debt securities, with evidence of deterioration of credit quality since origination that were acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable.

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-Publisher AICPA

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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 total undiscounted amount of all uncollected contractual principal and contractual interest payments both past due and scheduled for the future, adjusted for the timing of prepayments, if considered, less any reduction by the investor at the acquisition date. This relates to loans accounted for as available-for-sale debt securities, with evidence of deterioration of credit quality since origination that were acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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