Securitizations and Variable Interest Entities - Carrying amount of variable interests of unconsolidated VIEs and maximum exposure to loss (Detail) - JPY (¥) ¥ in Billions	Mar. 31, 2017	Mar. 31, 2016
Variable Interest Entity [Line Items]
Carrying amount of variable interests, Assets	¥ 4,496	¥ 4,126
Carrying amount of variable interests, Liabilities
Maximum exposure to loss to unconsolidated VIEs	4,557	4,170
Equities [Member]
Variable Interest Entity [Line Items]
Carrying amount of variable interests, Assets	65	87
Carrying amount of variable interests, Liabilities
Maximum exposure to loss to unconsolidated VIEs	65	87
Debt securities [Member]
Variable Interest Entity [Line Items]
Carrying amount of variable interests, Assets	109	118
Carrying amount of variable interests, Liabilities
Maximum exposure to loss to unconsolidated VIEs	109	118
CMBS and RMBS
Variable Interest Entity [Line Items]
Carrying amount of variable interests, Assets	3,754	3,067
Carrying amount of variable interests, Liabilities
Maximum exposure to loss to unconsolidated VIEs	3,754	3,067
Investment trust funds and other [Member]
Variable Interest Entity [Line Items]
Carrying amount of variable interests, Assets	146	413
Carrying amount of variable interests, Liabilities
Maximum exposure to loss to unconsolidated VIEs	146	413
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	24	14
Carrying amount of variable interests, Liabilities
Maximum exposure to loss to unconsolidated VIEs	24	14
Loans [Member]
Variable Interest Entity [Line Items]
Carrying amount of variable interests, Assets	388	423
Carrying amount of variable interests, Liabilities
Maximum exposure to loss to unconsolidated VIEs	388	423
Other [Member]
Variable Interest Entity [Line Items]
Carrying amount of variable interests, Assets	10	4
Carrying amount of variable interests, Liabilities
Maximum exposure to loss to unconsolidated VIEs	10	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	¥ 59	¥ 42

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=64801991&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=64801991&loc=d3e5747-111685

+ Details

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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.

+ Details

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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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