Property, Plant and Equipment (Details Textual) (USD $) In Millions, unless otherwise specified	12 Months Ended
Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2013
Property, Plant and Equipment [Abstract]
Fully depreciated assets	$ 756nvl_FullyDepreciatedAssets	$ 752nvl_FullyDepreciatedAssets
Capitalized interest costs	$ 20us-gaap_InterestCostsCapitalized	$ 33us-gaap_InterestCostsCapitalized	$ 36us-gaap_InterestCostsCapitalized
Capital leases, term of contract	15 years

Amount of interest capitalized during the period.

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Allowance for Funds Used during Construction

-URI http://asc.fasb.org/extlink&oid=6504829

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6450988&loc=d3e26243-108391

Name:	us-gaap_InterestCostsCapitalized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration