Investments in Affiliates - Additional Information (Detail) - JPY (¥) ¥ in Millions	Mar. 31, 2016	Mar. 31, 2015
Schedule of Equity Method Investments [Line Items]
Amount pledged as collateral	¥ 3,040	¥ 1,489
Kagoshima Mega Solar Power
Schedule of Equity Method Investments [Line Items]
Loans secured by collateral	19,490
Equity Method Investments \| Kagoshima Mega Solar Power
Schedule of Equity Method Investments [Line Items]
Amount pledged as collateral	¥ 1,781

Face (par) amount of debt instrument at time of issuance.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=34725769&loc=d3e28878-108400

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399

Name:	us-gaap_DebtInstrumentFaceAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant