Outstanding Exposure - Financial Guaranty Portfolio by Internal Rating (Details) (USD $) In Millions, unless otherwise specified													3 Months Ended
	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2014 Public Finance U.S.	Dec. 31, 2013 Public Finance U.S.	Mar. 31, 2014 Public Finance Non-U.S.	Dec. 31, 2013 Public Finance Non-U.S.	Mar. 31, 2014 Structured Finance U.S.	Dec. 31, 2013 Structured Finance U.S.	Mar. 31, 2014 Structured Finance Non-U.S.	Dec. 31, 2013 Structured Finance Non-U.S.	Mar. 31, 2014 Structured finance	Mar. 31, 2014 Public finance	Mar. 31, 2013 Public finance Minimum	Mar. 31, 2013 Public finance Maximum	Mar. 31, 2014 AAA	Dec. 31, 2013 AAA	Mar. 31, 2014 AAA Public Finance U.S.	Dec. 31, 2013 AAA Public Finance U.S.	Mar. 31, 2014 AAA Public Finance Non-U.S.	Dec. 31, 2013 AAA Public Finance Non-U.S.	Mar. 31, 2014 AAA Structured Finance U.S.	Dec. 31, 2013 AAA Structured Finance U.S.	Mar. 31, 2014 AAA Structured Finance Non-U.S.	Dec. 31, 2013 AAA Structured Finance Non-U.S.	Mar. 31, 2014 AA	Dec. 31, 2013 AA	Mar. 31, 2014 AA Public Finance U.S.	Dec. 31, 2013 AA Public Finance U.S.	Mar. 31, 2014 AA Public Finance Non-U.S.	Dec. 31, 2013 AA Public Finance Non-U.S.	Mar. 31, 2014 AA Structured Finance U.S.	Dec. 31, 2013 AA Structured Finance U.S.	Mar. 31, 2014 AA Structured Finance Non-U.S.	Dec. 31, 2013 AA Structured Finance Non-U.S.	Mar. 31, 2014 A	Dec. 31, 2013 A	Mar. 31, 2014 A Public Finance U.S.	Dec. 31, 2013 A Public Finance U.S.	Mar. 31, 2014 A Public Finance Non-U.S.	Dec. 31, 2013 A Public Finance Non-U.S.	Mar. 31, 2014 A Structured Finance U.S.	Dec. 31, 2013 A Structured Finance U.S.	Mar. 31, 2014 A Structured Finance Non-U.S.	Dec. 31, 2013 A Structured Finance Non-U.S.	Mar. 31, 2014 BBB	Dec. 31, 2013 BBB	Mar. 31, 2014 BBB Public Finance U.S.	Dec. 31, 2013 BBB Public Finance U.S.	Mar. 31, 2014 BBB Public Finance Non-U.S.	Dec. 31, 2013 BBB Public Finance Non-U.S.	Mar. 31, 2014 BBB Structured Finance U.S.	Dec. 31, 2013 BBB Structured Finance U.S.	Mar. 31, 2014 BBB Structured Finance Non-U.S.	Dec. 31, 2013 BBB Structured Finance Non-U.S.	Mar. 31, 2014 Below investment grade (BIG)	Dec. 31, 2013 Below investment grade (BIG)	Mar. 31, 2014 Below investment grade (BIG) Public Finance U.S.	Dec. 31, 2013 Below investment grade (BIG) Public Finance U.S.	Mar. 31, 2014 Below investment grade (BIG) Public Finance Non-U.S.	Dec. 31, 2013 Below investment grade (BIG) Public Finance Non-U.S.	Mar. 31, 2014 Below investment grade (BIG) Structured Finance U.S.	Dec. 31, 2013 Below investment grade (BIG) Structured Finance U.S.	Mar. 31, 2014 Below investment grade (BIG) Structured Finance Non-U.S.	Dec. 31, 2013 Below investment grade (BIG) Structured Finance Non-U.S.	Mar. 31, 2014 Loss Mitigation Bonds [Member] Below investment grade (BIG)	Dec. 31, 2013 Loss Mitigation Bonds [Member] Below investment grade (BIG)	Mar. 31, 2014 Loss Mitigation Bonds [Member] Below investment grade (BIG) Public Finance U.S.	Dec. 31, 2013 Loss Mitigation Bonds [Member] Below investment grade (BIG) Public Finance U.S.	Mar. 31, 2014 Loss Mitigation Bonds [Member] Below investment grade (BIG) Public Finance Non-U.S.	Dec. 31, 2013 Loss Mitigation Bonds [Member] Below investment grade (BIG) Public Finance Non-U.S.	Mar. 31, 2014 Loss Mitigation Bonds [Member] Below investment grade (BIG) Structured Finance U.S.	Dec. 31, 2013 Loss Mitigation Bonds [Member] Below investment grade (BIG) Structured Finance U.S.	Mar. 31, 2014 Loss Mitigation Bonds [Member] Below investment grade (BIG) Structured Finance Non-U.S.	Dec. 31, 2013 Loss Mitigation Bonds [Member] Below investment grade (BIG) Structured Finance Non-U.S.
Financial guarantee obligations
Net Par Amount Outstanding	$ 449,625	$ 459,107	$ 346,428	$ 352,181	$ 34,826	$ 33,998	$ 55,393	$ 58,907	$ 12,978	$ 14,021					$ 44,402	$ 48,015	$ 4,658	$ 4,998	$ 1,020	$ 1,016	$ 29,868	$ 32,317	$ 8,856	$ 9,684	$ 114,970	$ 117,933	$ 104,577	$ 107,503	$ 427	$ 422	$ 9,396	$ 9,431	$ 570	$ 577	$ 200,029	$ 205,616	$ 187,433	$ 192,841	$ 9,595	$ 9,453	$ 2,340	$ 2,580	$ 661	$ 742	$ 68,281	$ 65,005	$ 40,783	$ 37,745	$ 22,173	$ 21,499	$ 3,496	$ 3,815	$ 1,829	$ 1,946	$ 21,943	$ 22,538	$ 8,977	$ 9,094	$ 1,611	$ 1,608	$ 10,293	$ 10,764	$ 1,062	$ 1,072
Insured Financial Obligations Outstanding Principal Amount	450,861	460,302	346,460	352,213	34,826	33,998	56,597	60,070	12,978	14,021																																																							1,236	1,195	32	32	0	0	1,204	1,163	0	0
% of Total Net Par Outstanding	100.00%	100.00%	100.00%	100.00%	100.00%	100.00%	100.00%	100.00%	100.00%	100.00%					9.90%	10.50%	1.30%	1.40%	2.90%	3.00%	53.90%	54.90%	68.20%	69.10%	25.60%	25.70%	30.20%	30.50%	1.20%	1.20%	17.00%	16.00%	4.40%	4.10%	44.40%	44.80%	54.10%	54.80%	27.60%	27.90%	4.20%	4.40%	5.10%	5.30%	15.20%	14.10%	11.80%	10.70%	63.70%	63.20%	6.30%	6.40%	14.10%	13.90%	4.90%	4.90%	2.60%	2.60%	4.60%	4.70%	18.60%	18.30%	8.20%	7.60%
Securities purchased to settle credit derivative contracts	165	195
Outstanding commitments to provide guaranties											577	330
Expiration date for insured financial obligation commitments													Apr. 15, 2014	Feb. 25, 2017
Outstanding commitments to provide guaranties, amount expiring prior to December 31, 2012												$ 206