Supplemental Condensed Consolidating Financial Information - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Mar. 31, 2014	Dec. 06, 2012 Senior Unsecured Notes Due 2021 [Member]	Nov. 23, 2010 Senior Unsecured Notes Due 2021 [Member]
Supplemental Condensed Consolidating Financial Information [Line Items]
Debt instrument, principal amount		$ 3,500	$ 1,000	$ 1,525
Debt instrument, stated interest			6.25%	7.75%
Ownership percentage held by parent	100.00%

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 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399

Reference 2: 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

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