Variable Interest Entities (CLN structures summary information) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012
Credit Linked Note Structure December 2006 [Member]
Credit Linked Notes Structures Summary Information [Line Items]
Amount of Issuance	$ 400
Date of Issuance	December 2006
Original attachment point (subordination)	5.50%
Current attachment point (subordination)	4.17%
Maturity	12/20/2016
Current rating of tranche	BB-
Current rating of underlying collateral pool, high end of range	Aa1
Current rating of underlying collateral pool, low end of range	B3
Number of defaults in underlying collateral pool	2
Number of entities	123
Number of countries	20
Credit Linked Note Structure April 2007 [Member]
Credit Linked Notes Structures Summary Information [Line Items]
Amount of Issuance	$ 200
Date of Issuance	April 2007
Original attachment point (subordination)	2.05%
Current attachment point (subordination)	1.48%
Maturity	3/20/2017
Current rating of tranche	Ba2
Current rating of underlying collateral pool, high end of range	Aaa
Current rating of underlying collateral pool, low end of range	Caa2
Number of defaults in underlying collateral pool	2
Number of entities	99
Number of countries	21