Non-trading securities - Additional Information (Detail) - Insurance subsidiary [Member] ¥ in Millions	12 Months Ended
Mar. 31, 2015 JPY (¥)	Mar. 31, 2014 JPY (¥)
Non-trading debt securities [Line Items]
Non-trading securities disposed	¥ 75,745	¥ 138,231
Non-trading securities realized gain	5,008	4,405
Non-trading securities realized loss	15	81
Total proceeds received from disposals	¥ 80,738	¥ 142,554
Total number of non-trading securities that are in an unrealized loss positions	26	60
Other-than-temporary impairment loss recognized for non-trading equity securities	¥ 16	¥ 79
Credit loss component of other-than-temporary impairment losses recognized for non-trading debt securities	98	25
Other-than-temporary impairment loss recognized within other comprehensive income (loss)	¥ 31	¥ (55)

Available For Sale Securities Continuous Unrealized Loss Position Number Of Securities

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For any sales of securities categorized neither as held-to-maturity nor trading, this item represents the net carrying amount of the sold security.

+ References

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- Definition

This item represents the gain realized on the sale of securities categorized neither as held-to-maturity nor trading disposed of during the period.

+ References

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This item represents the loss realized on the sale of securities categorized neither as held-to-maturity nor trading disposed of during the period.

+ References

No definition available.

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- Definition

The credit loss component of other-than-temporary impairment losses recognized for non-trading debt securities

+ References

No definition available.

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- Definition

The total amount of proceeds received for the sale of securities, categorized neither as held-to-maturity nor trading securities, during the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 9

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- Definition

Amount before tax of other than temporary impairment (OTTI) loss on investments in available-for-sale and held-to-maturity debt securities, recognized in other comprehensive loss.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 220

-SubTopic 10

-Section 45

-Paragraph 10A

-Subparagraph (g)

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 35

-Paragraph 35

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- Definition

The amount of other than temporary impairment (OTTI) losses on equity securities, OTTI related to credit losses on debt securities, and OTTI losses on debt securities when the entity intends to sell the securities or it is more likely than not that the entity will be required to sell the securities before recovery of its amortized cost basis. Additionally, this item includes OTTI losses recognized during the period on investments accounted for under the cost method of accounting.

+ References

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 8B

-URI http://asc.fasb.org/extlink&oid=27724398&loc=SL6284393-111563

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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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