Guaranteed Benefit Features - Guaranteed Death and Benefit (Parenthetical) (Detail) (Separate Account Liability, Stabilizer / MCG, USD $) In Billions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Separate Account Liability \| Stabilizer / MCG
Liabilities for Guarantees on Long-Duration Contracts [Line Items]
Externally managed assets included in Separate account liability not reported on balance sheet	$ 25.9	$ 24.2

The face amount of financial liabilities, which are not recognized in the financial statements (off-balance sheet) because they fail to meet some other criterion for recognition.

No definition available.

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