Securitizations and Variable Interest Entities - Carrying Amount of Assets and Liabilities of Unconsolidated VIEs (Detail) - JPY (¥) ¥ in Billions	Sep. 30, 2015	Mar. 31, 2015
Variable Interest Entity [Line Items]
Carrying amount of variable interests, Assets	¥ 3,748	¥ 3,610
Carrying amount of variable interests, Liabilities
Maximum exposure to loss to unconsolidated VIEs	¥ 3,819	¥ 3,652
Equities [Member]
Variable Interest Entity [Line Items]
Carrying amount of variable interests, Assets	¥ 129	¥ 123
Carrying amount of variable interests, Liabilities
Maximum exposure to loss to unconsolidated VIEs	¥ 129	¥ 123
Debt securities [Member]
Variable Interest Entity [Line Items]
Carrying amount of variable interests, Assets	¥ 215	¥ 237
Carrying amount of variable interests, Liabilities
Maximum exposure to loss to unconsolidated VIEs	¥ 215	¥ 237
CMBS and RMBS
Variable Interest Entity [Line Items]
Carrying amount of variable interests, Assets	¥ 2,750	¥ 2,521
Carrying amount of variable interests, Liabilities
Maximum exposure to loss to unconsolidated VIEs	¥ 2,750	¥ 2,521
Investment trust funds and other [Member]
Variable Interest Entity [Line Items]
Carrying amount of variable interests, Assets	¥ 290	¥ 387
Carrying amount of variable interests, Liabilities
Maximum exposure to loss to unconsolidated VIEs	¥ 290	¥ 387
Derivatives [Member]
Variable Interest Entity [Line Items]
Carrying amount of variable interests, Assets	¥ 0	¥ 0
Carrying amount of variable interests, Liabilities
Maximum exposure to loss to unconsolidated VIEs	¥ 2	¥ 2
Private equity investments [Member]
Variable Interest Entity [Line Items]
Carrying amount of variable interests, Assets	¥ 25	¥ 24
Carrying amount of variable interests, Liabilities
Maximum exposure to loss to unconsolidated VIEs	¥ 25	¥ 24
Loans [Member]
Variable Interest Entity [Line Items]
Carrying amount of variable interests, Assets	¥ 335	¥ 314
Carrying amount of variable interests, Liabilities
Maximum exposure to loss to unconsolidated VIEs	¥ 335	¥ 314
Other [Member]
Variable Interest Entity [Line Items]
Carrying amount of variable interests, Assets	¥ 4	¥ 4
Carrying amount of variable interests, Liabilities
Maximum exposure to loss to unconsolidated VIEs	¥ 4	¥ 4
Commitments to extend credit and other guarantees [Member]
Variable Interest Entity [Line Items]
Carrying amount of variable interests, Assets
Carrying amount of variable interests, Liabilities
Maximum exposure to loss to unconsolidated VIEs	¥ 69	¥ 40

The reporting entity's maximum amount of exposure to loss as a result of its involvement with the Variable Interest Entity (VIE).

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph b
-URI http://asc.fasb.org/extlink&oid=52262685&loc=d3e5728-111685

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=52262685&loc=d3e5747-111685

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- Definition

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.

+ References

No definition available.

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- Definition

Carrying amount of the assets in the reporting entity's statement of financial position that relate to the reporting entity's variable interest in the Variable Interest Entity (VIE), where the reporting entity is not the VIE's primary beneficiary.

+ References

+ Details

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- Definition

Carrying amount of the liabilities in the reporting entity's statement of financial position that relate to the reporting entity's variable interest in the Variable Interest Entity (VIE), where the reporting entity is not the VIE's primary beneficiary.

+ References

+ Details

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