Investments and Derivative Instruments (Details Textuals 2) (USD $) In Millions	Jun. 30, 2011	Dec. 31, 2010
Variable Interest Entity [Line Items]
Other liabilities, variable interest entity liabilities	$ 439	$ 394
Non-Consolidated VIEs [Member]
Variable Interest Entity [Line Items]
Assets	30	32
Other liabilities, variable interest entity liabilities	30	32
Company's maximum exposure to the loss of the contingent capital facility	$ 4	$ 4

Quantifies the net carrying amount of the entity's assets.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name FASB Staff Position (FSP)
-Number FAS140-4 and FIN46(R)-8
-Paragraph C6
-Subparagraph c

+ Details

Name:	us-gaap_VariableInterestCarryingAmountAssets
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Quantifies the net carrying amount of the entity's liabilities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name FASB Staff Position (FSP)
-Number FAS140-4 and FIN46(R)-8
-Paragraph C6
-Subparagraph c

+ Details

Name:	us-gaap_VariableInterestCarryingAmountLiabilities
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ Details

Name:	us-gaap_VariableInterestEntityLineItems
Namespace Prefix:	us-gaap
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Quantifies the entity's maximum exposure to loss.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name FASB Staff Position (FSP)
-Number FAS140-4 and FIN46(R)-8
-Paragraph C6
-Subparagraph c

+ Details

Name:	us-gaap_VariableInterestMaximumExposureToLoss
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant