Securitizations and Variable Interest Entities - Carrying amount of variable interests of unconsolidated VIEs and maximum exposure to loss (Detail) - JPY (¥) ¥ in Billions	Sep. 30, 2017	Mar. 31, 2017
Variable Interest Entity [Line Items]
Carrying amount of variable interests, Assets	¥ 3,964	¥ 4,496
Carrying amount of variable interests, Liabilities
Maximum exposure to loss to unconsolidated VIEs	4,026	4,557
Equities [Member]
Variable Interest Entity [Line Items]
Carrying amount of variable interests, Assets	55	65
Carrying amount of variable interests, Liabilities
Maximum exposure to loss to unconsolidated VIEs	55	65
Debt securities [Member]
Variable Interest Entity [Line Items]
Carrying amount of variable interests, Assets	110	109
Carrying amount of variable interests, Liabilities
Maximum exposure to loss to unconsolidated VIEs	110	109
CMBS and RMBS [Member]
Variable Interest Entity [Line Items]
Carrying amount of variable interests, Assets	3,169	3,754
Carrying amount of variable interests, Liabilities
Maximum exposure to loss to unconsolidated VIEs	3,169	3,754
Investment trust funds and other [Member]
Variable Interest Entity [Line Items]
Carrying amount of variable interests, Assets	210	146
Carrying amount of variable interests, Liabilities
Maximum exposure to loss to unconsolidated VIEs	210	146
Derivatives [Member]
Variable Interest Entity [Line Items]
Carrying amount of variable interests, Assets		0
Carrying amount of variable interests, Liabilities
Maximum exposure to loss to unconsolidated VIEs		2
Private equity investments [Member]
Variable Interest Entity [Line Items]
Carrying amount of variable interests, Assets	17	24
Carrying amount of variable interests, Liabilities
Maximum exposure to loss to unconsolidated VIEs	17	24
Loans [Member]
Variable Interest Entity [Line Items]
Carrying amount of variable interests, Assets	385	388
Carrying amount of variable interests, Liabilities
Maximum exposure to loss to unconsolidated VIEs	385	388
Other [Member]
Variable Interest Entity [Line Items]
Carrying amount of variable interests, Assets	18	10
Carrying amount of variable interests, Liabilities
Maximum exposure to loss to unconsolidated VIEs	18	10
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	¥ 62	¥ 59

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=77990344&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=77990344&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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