Investments Mortgage Loan Restructuring (Detail) (Commercial Real Estate Portfolio Segment [Member])	3 Months Ended	6 Months Ended
Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Commercial Real Estate Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Carrying Amount	8.9	0	13.1	9.8
Financing Receivables, modifications, number of contracts	1	0	2	1

Voluntary or miscellaneous disclosures regarding a troubled debt restructuring, not otherwise listed in the existing taxonomy.

No definition available.

Name:	us-gaap_TroubledDebtRestructuringDebtorOther
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration