Derivative Instruments (Collateral Support Agreements) (Details) - Open Credit Default Swap Liabilities [Member] - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Credit risk related contingent features collateral
Maximum potential payout	$ 103	$ 126
Less: Counterparty thresholds
Maximum collateral potentially required to post	$ 103	$ 126

Maximum potential amount of future undiscounted payments that could be required under the credit derivative, before reduction for potential recoveries under recourse or collateralization provisions.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4K

-Subparagraph (b)(1)

-URI http://asc.fasb.org/extlink&oid=35706170&loc=SL5708775-113959

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Credit Derivative

-URI http://asc.fasb.org/extlink&oid=6854095

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