Investments Mortgage Loan Restructuring (Detail) (Commercial Real Estate Portfolio Segment [Member], USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Mar. 31, 2011
Commercial Real Estate Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Carrying Amount	$ 4.2	$ 9.8
Number of Loans	1	1

The amount of the outstanding recorded investment related to financing receivables that have been modified by troubled debt restructurings before the financing receivable has been modified.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 32

-URI http://asc.fasb.org/extlink&oid=6965416&loc=SL6953670-111524

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 33

-URI http://asc.fasb.org/extlink&oid=6965416&loc=SL6953676-111524

Name:	us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant