Non-trading securities - Non-Trading securities Reconciliation (Detail) (Insurance subsidiary [Member], JPY ¥) In Millions, unless otherwise specified	Mar. 31, 2013	Mar. 31, 2012
Non-trading debt securities [Line Items]
Cost and/or amortized cost	¥ 271,403	¥ 240,917
Gross unrealized gains	18,943	3,754
Gross unrealized losses	321	2,415
Fair value	290,025	242,256
Government, agency and municipal securities [Member]
Non-trading debt securities [Line Items]
Cost and/or amortized cost	177,374	150,203
Gross unrealized gains	5,294	445
Gross unrealized losses	126	164
Fair value	182,542	150,484
Other debt securities [Member]
Non-trading debt securities [Line Items]
Cost and/or amortized cost	54,032	37,356
Gross unrealized gains	726	115
Gross unrealized losses	86	182
Fair value	54,672	37,289
Equity securities [Member]
Non-trading debt securities [Line Items]
Cost and/or amortized cost	39,997	53,358
Gross unrealized gains	12,923	3,194
Gross unrealized losses	109	2,069
Fair value	¥ 52,811	¥ 54,483

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents Available-for-sale Securities which consist of all investments in certain debt and equity securities neither classified as trading or held-to-maturity securities. A debt security represents a creditor relationship with an enterprise. Debt securities include, among other items, US Treasury securities, US government securities, municipal securities, corporate bonds, convertible debt, commercial paper, and all securitized debt instruments. An equity security represents an ownership interest in an enterprise or the right to acquire or dispose of an ownership interest in an enterprise at fixed or determinable prices. Equity securities include, among other things, common stock, certain preferred stock, warrant rights, call options, and put options, but do not include convertible debt. An entity may opt to provide the reader with additional narrative text to better understand the nature of investments in debt and equity securities which are categorized as Available-for-sale.

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- Definition

This item represents the gross unrealized gains for securities, at a point in time, which are categorized neither as held-to-maturity nor trading securities.

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