Discontinued Operations - Additional Information (Detail) - JPY (¥) ¥ in Millions	12 Months Ended
Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2013
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gains (losses) on sales of subsidiaries and liquidation losses, net			¥ (13)
Property under Facility Operations	¥ 278,100	¥ 295,863
Trade Notes, Accounts and Other Receivable	348,404	193,369
Other Assets	1,464,203	1,222,214
Trade Notes, Accounts and Other Payable	335,936	263,823
Long-Term Debt	4,132,945	3,852,668
Assets	11,443,628	9,066,961	8,439,710
Gains on sales of real estate properties	34,425	23,692	19,848
Accounting Standards Codification 205-20
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gains (losses) on sales of subsidiaries and liquidation losses, net		(1,600)
Subsidiaries
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gains losses on derivative trading instruments included in income from subsidiary			(370)
Segment, Discontinued Operations \| Accounting Standards Codification 205-20
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gains (losses) on sales of subsidiaries and liquidation losses, net	362
Property under Facility Operations		1,561
Trade Notes, Accounts and Other Receivable		2,066
Other Assets		1,511
Trade Notes, Accounts and Other Payable		1,822
Long-Term Debt		1,336
Assets	0
Real Estate One
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gains on sales of real estate properties	0	16,200	¥ 6,802
Rental properties held for sale	24,619	42,266
Real Estate One \| Property under Facility Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Rental properties held for sale	2,873	¥ 2,428
Real Estate One \| Other assets
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Rental properties held for sale	¥ 689

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Property under Facility Operations

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Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

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Carrying amount of long-term debt, net of unamortized discount or premium, including current and noncurrent amounts. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Carrying amount as of the balance sheet date of investments in land and buildings held for sale, excluding real estate considered to be inventory of the entity.

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