Outstanding Exposure - Financial Guaranty Portfolio by Internal Rating (Details) (USD $) In Millions, unless otherwise specified													9 Months Ended
	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2014 Public Finance U.S.	Dec. 31, 2013 Public Finance U.S.	Sep. 30, 2014 Public Finance Non-U.S.	Dec. 31, 2013 Public Finance Non-U.S.	Sep. 30, 2014 Structured Finance U.S.	Dec. 31, 2013 Structured Finance U.S.	Sep. 30, 2014 Structured Finance Non-U.S.	Dec. 31, 2013 Structured Finance Non-U.S.	Sep. 30, 2014 Structured finance	Sep. 30, 2014 Public finance	Sep. 30, 2014 Public finance Minimum	Sep. 30, 2014 Public finance Maximum	Sep. 30, 2014 AAA	Dec. 31, 2013 AAA	Sep. 30, 2014 AAA Public Finance U.S.	Dec. 31, 2013 AAA Public Finance U.S.	Sep. 30, 2014 AAA Public Finance Non-U.S.	Dec. 31, 2013 AAA Public Finance Non-U.S.	Sep. 30, 2014 AAA Structured Finance U.S.	Dec. 31, 2013 AAA Structured Finance U.S.	Sep. 30, 2014 AAA Structured Finance Non-U.S.	Dec. 31, 2013 AAA Structured Finance Non-U.S.	Sep. 30, 2014 AA	Dec. 31, 2013 AA	Sep. 30, 2014 AA Public Finance U.S.	Dec. 31, 2013 AA Public Finance U.S.	Sep. 30, 2014 AA Public Finance Non-U.S.	Dec. 31, 2013 AA Public Finance Non-U.S.	Sep. 30, 2014 AA Structured Finance U.S.	Dec. 31, 2013 AA Structured Finance U.S.	Sep. 30, 2014 AA Structured Finance Non-U.S.	Dec. 31, 2013 AA Structured Finance Non-U.S.	Sep. 30, 2014 A	Dec. 31, 2013 A	Sep. 30, 2014 A Public Finance U.S.	Dec. 31, 2013 A Public Finance U.S.	Sep. 30, 2014 A Public Finance Non-U.S.	Dec. 31, 2013 A Public Finance Non-U.S.	Sep. 30, 2014 A Structured Finance U.S.	Dec. 31, 2013 A Structured Finance U.S.	Sep. 30, 2014 A Structured Finance Non-U.S.	Dec. 31, 2013 A Structured Finance Non-U.S.	Sep. 30, 2014 BBB	Dec. 31, 2013 BBB	Sep. 30, 2014 BBB Public Finance U.S.	Dec. 31, 2013 BBB Public Finance U.S.	Sep. 30, 2014 BBB Public Finance Non-U.S.	Dec. 31, 2013 BBB Public Finance Non-U.S.	Sep. 30, 2014 BBB Structured Finance U.S.	Dec. 31, 2013 BBB Structured Finance U.S.	Sep. 30, 2014 BBB Structured Finance Non-U.S.	Dec. 31, 2013 BBB Structured Finance Non-U.S.	Sep. 30, 2014 Below investment grade (BIG)	Dec. 31, 2013 Below investment grade (BIG)	Sep. 30, 2014 Below investment grade (BIG) Public Finance U.S.	Dec. 31, 2013 Below investment grade (BIG) Public Finance U.S.	Sep. 30, 2014 Below investment grade (BIG) Public Finance Non-U.S.	Dec. 31, 2013 Below investment grade (BIG) Public Finance Non-U.S.	Sep. 30, 2014 Below investment grade (BIG) Structured Finance U.S.	Dec. 31, 2013 Below investment grade (BIG) Structured Finance U.S.	Sep. 30, 2014 Below investment grade (BIG) Structured Finance Non-U.S.	Dec. 31, 2013 Below investment grade (BIG) Structured Finance Non-U.S.	Sep. 30, 2014 Loss Mitigation Bonds Below investment grade (BIG)	Dec. 31, 2013 Loss Mitigation Bonds Below investment grade (BIG)	Sep. 30, 2014 Loss Mitigation Bonds Below investment grade (BIG) Public Finance U.S.	Dec. 31, 2013 Loss Mitigation Bonds Below investment grade (BIG) Public Finance U.S.	Sep. 30, 2014 Loss Mitigation Bonds Below investment grade (BIG) Public Finance Non-U.S.	Dec. 31, 2013 Loss Mitigation Bonds Below investment grade (BIG) Public Finance Non-U.S.	Sep. 30, 2014 Loss Mitigation Bonds Below investment grade (BIG) Structured Finance U.S.	Dec. 31, 2013 Loss Mitigation Bonds Below investment grade (BIG) Structured Finance U.S.	Sep. 30, 2014 Loss Mitigation Bonds Below investment grade (BIG) Structured Finance Non-U.S.	Dec. 31, 2013 Loss Mitigation Bonds Below investment grade (BIG) Structured Finance Non-U.S.
Financial guarantee obligations
Net par amount outstanding	$ 418,015	$ 459,107	$ 329,225	$ 352,181	$ 33,487	$ 33,998	$ 44,874	$ 58,907	$ 10,429	$ 14,021					$ 34,819	$ 48,015	$ 4,173	$ 4,998	$ 1,011	$ 1,016	$ 23,193	$ 32,317	$ 6,442	$ 9,684	$ 105,149	$ 117,933	$ 96,107	$ 107,503	$ 388	$ 422	$ 8,115	$ 9,431	$ 539	$ 577	$ 190,342	$ 205,616	$ 178,484	$ 192,841	$ 9,451	$ 9,453	$ 1,849	$ 2,580	$ 558	$ 742	$ 68,059	$ 65,005	$ 41,919	$ 37,745	$ 21,159	$ 21,499	$ 3,044	$ 3,815	$ 1,937	$ 1,946	$ 19,646	$ 22,538	$ 8,542	$ 9,094	$ 1,478	$ 1,608	$ 8,673	$ 10,764	$ 953	$ 1,072
Net par amount outstanding including loss mitigation bonds	419,304	460,302	329,254	352,213	33,487	33,998	46,134	60,070	10,429	14,021																																																							1,289	1,195	29	32	0	0	1,260	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%					8.30%	10.50%	1.30%	1.40%	3.00%	3.00%	51.70%	54.90%	61.80%	69.10%	25.20%	25.70%	29.20%	30.50%	1.20%	1.20%	18.10%	16.00%	5.20%	4.10%	45.50%	44.80%	54.20%	54.80%	28.20%	27.90%	4.10%	4.40%	5.40%	5.30%	16.30%	14.10%	12.70%	10.70%	63.20%	63.20%	6.80%	6.40%	18.50%	13.90%	4.70%	4.90%	2.60%	2.60%	4.40%	4.70%	19.30%	18.30%	9.10%	7.60%
Outstanding commitments to provide guaranties											294	459
Expiration date for insured financial obligation commitments													Oct. 01, 2014	Feb. 25, 2017
Outstanding commitments to provide guaranties, amount expiring prior to December 31, 2014												$ 335