Investment in Securities - Additional Information (Detail) In Millions, unless otherwise specified	12 Months Ended		12 Months Ended
Mar. 31, 2011 USD ($) Year Investment	Mar. 31, 2011 JPY (¥)	Mar. 31, 2010 JPY (¥)	Mar. 31, 2009 JPY (¥)	Mar. 31, 2010 Investment	Mar. 31, 2011 CMBS and RMBS in the U.S., and other asset-backed securities USD ($)	Mar. 31, 2011 CMBS and RMBS in the U.S., and other asset-backed securities JPY (¥)	Mar. 31, 2010 CMBS and RMBS in the U.S., and other asset-backed securities JPY (¥)
Schedule of Investments [Line Items]
Net unrealized holding gains (losses) on trading securities	$ 25	¥ 2,065	¥ 7,211	¥ (13,065)
Proceeds from sales of available-for-sale securities	4,095	340,634	181,033	242,702
Available-for-sale securities gross realized gains	67	5,579	7,547	8,266
Available-for-sale securities gross realized Losses	8	712	640	4,932
Write-downs of securities	262	21,749	23,634	18,574
Interest income on investment securities	213	17,690	20,436	23,758
Aggregate carrying amount of other securities accounted for under the cost method	810	67,366	72,347
Aggregate carrying amount of other securities not evaluated for impairment	765	63,590	62,208
Carrying amount of debt securities acquired with evidence of deterioration of credit quality	92	7,612	11,880
Nominal value of debt securities acquired with evidence of deterioration of credit quality	218	18,090	40,605
Outstanding balance of accretable yield of debt securities acquired with evidence of deterioration of credit quality	75	6,202	10,420
Non-credit components of other-than-temporary impairments						$ 5	¥ 392	¥ 1,638
Approximate number of investment securities in an unrealized loss position	449	449			411

Gross unrealized loss of noncredit portion of other than temporary impairments.

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Number of Securities, Unrealized Losses Position

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This item represents the gross profit realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities.

+ References

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-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 115
-Paragraph 21
-Subparagraph a

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This item represents the gross loss realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities.

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-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
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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 for loans accounted for as 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
-Name Statement of Position (SOP)
-Number 03-3
-Paragraph 16
-Subparagraph a(2)

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The recorded balance, net of any applicable reductions (for example, unamortized accreditable yield and other-than-temporary impairments), for certain contractual rights to receive money on demand or on fixed or determinable dates (that is, loans) accounted for as 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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-Name Statement of Position (SOP)
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-Paragraph 16
-Subparagraph a(1)

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For loans accounted for as 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, that have a net carrying amount, the undiscounted sum of all amounts, including amounts deemed principal, interest, fees, penalties, and other under the loan, owed to the investor at the reporting date, whether or not currently due and whether or not any such amounts have been written or charged off by the investor. Amounts forgiven in a debt restructuring but contingently payable to the investor should be included in the forgiven contract balance, but amounts irrevocably forgiven in a debt restructuring should not be included. Amounts payable to the investor in cash, in kind, and by any other means should be included. Amounts legally discharged should not be included. The outstanding balance does not include amounts that would be accrued under the contract as interest, fees, penalties, and other after the reporting date.

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This element represents the aggregate carrying amount of all cost-method investments held by the Company. Generally, such investments do not have readily determinable fair values and are not required to be accounted for by the equity method. The carrying amount of such securities equates to cost, adjusted for other-than-temporary impairment. The cost method and lower-of-cost or market, an adaptation of the cost method, is generally followed for most investments in noncontrolled corporations, in some corporate joint ventures, and to a lesser extent in unconsolidated subsidiaries, particularly foreign.

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-Publisher FASB
-Name Emerging Issues Task Force (EITF)
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This element represents the aggregate carrying amount of all cost-method investments held by the Entity which was not evaluated for impairment. Because the fair value of cost-method investments is not readily determinable, the evaluation of whether an investment is impaired generally consists of whether an event or change in circumstances has occurred during the reporting period that may have a significant adverse effect on the fair value of the investment (an "impairment indicator"). Impairment indicators include, but are not limited to: (1) significant deterioration in the earnings performance, credit rating, asset quality, or business prospects of the investee; (2) significant adverse change in the regulatory, economic, or technological environment of the investee; (3) significant adverse change in the general market condition of either the geographic area or the industry in which the investee operates; (4) a bona fide offer to purchase (whether solicited or unsolicited), an offer by the investee to sell, or a completed auction process for the same or similar security for an amount less than the cost of the investment; or (5) factors that raise significant concerns about the investee's ability to continue as a going concern, such as negative cash flows from operations, working capital deficiencies, or noncompliance with statutory capital requirements or debt covenants.

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This element represents the amount by which the carrying amount exceeds the fair value of the investment. The amount is charged to income if the decline in fair value is deemed to be other than temporary.

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Income derived from investments in debt securities and on cash and cash equivalents the earnings of which reflect the time value of money or transactions in which the payments are for the use or forbearance of money.

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-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 7
-Article 5

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The cash inflow associated with the sale of debt and equity securities classified as available-for-sale securities.

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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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For trading securities held as of the balance sheet date, this amount represents the difference between the fair value of trading securities and their carrying value (unrealized holding gain or loss). Trading securities are bought and held principally for the purpose of selling them in the near term (thus held for only a short period of time) and such unrealized holding gain or loss is included in earnings for the period.

+ References

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-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 115
-Paragraph 13

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-Publisher FASB
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