Non-trading securities - Additional Information (Detail) (JPY ¥) In Millions, unless otherwise specified	3 Months Ended	6 Months Ended
Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Mar. 31, 2014
Non-trading debt securities [Line Items]
Non-trading securities disposed	¥ 27,652	¥ 57,259	¥ 42,320	¥ 98,421
Non-trading securities realized gain	364	247	463	1,822
Non-trading securities realized loss	11	33	13	42
Total proceeds received from disposals	28,005	57,473	42,770	100,201
Total number of non-trading securities that are in an unrealized loss positions	20		20		60
Other-than-temporary impairment loss recognized for non-trading equity securities	12	39	15	47
Credit loss component of other-than-temporary impairment losses recognized for non-trading debt securities		23		25
Other-than-temporary impairment loss recognized within other comprehensive income (loss)	¥ (2)	¥ (60)	¥ 0	¥ (61)

Available For Sale Securities Continuous Unrealized Loss Position Number Of Securities

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- Definition

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

No definition available.

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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

No definition available.

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- Definition

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

-Subparagraph (a)

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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)

-URI http://asc.fasb.org/extlink&oid=36458714&loc=SL7669646-108580

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 35

-Paragraph 35

-URI http://asc.fasb.org/extlink&oid=27723805&loc=d3e25362-111560

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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

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

-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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