This item represents the aggregate carrying amount of all cost-method investments as reported on or included in the balance sheet. The original cost of the investments may differ from the aggregate carrying amount disclosed due to various adjustments such as: (i) dividends received in excess of earnings after the date of investment that are considered a return of investment and therefore recorded as reductions to cost of the investment, or (ii) a series of operating losses of an investee or other factors which may indicate that a decrease in value of the investment has occurred which is other than temporary and accordingly such decrease in value has been recognized.

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- Definition

The amount by which the fair value of an investment is less than the amortized cost basis or carrying amount of that investment at the balance sheet date and the decline in fair value is deemed to be other than temporary, before considering whether or not such amount is recognized in earnings or other comprehensive income.

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+ Details

Other Investments - Additional Information (Detail) (JPY ¥) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Mar. 31, 2010
Schedule of Available-for-sale Securities [Line Items]
Valuation losses on other investments recognized to reflect the decline in fair value	¥ 2,570	¥ 1,758	¥ 143
Conversion ratio of common shares			0.191
Gain on nonmonetary exchange of securities		2,774
Investments in non-traded and unaffiliated companies	9,306	10,025
MS&AD Insurance Group Holdings, Inc.
Schedule of Available-for-sale Securities [Line Items]
Fair value of common shares		4,140
Nissay Dowa General Insurance Co., Ltd
Schedule of Available-for-sale Securities [Line Items]
Carrying amount of common shares		¥ 1,366