Outstanding Exposure (Details 2) (USD $)																																																																																	6 Months Ended
	Jun. 30, 2012	Dec. 31, 2011	Jun. 30, 2012 Super senior	Dec. 31, 2011 Super senior	Jun. 30, 2012 AAA	Dec. 31, 2011 AAA	Jun. 30, 2012 AA	Dec. 31, 2011 AA	Jun. 30, 2012 AA Bank of America Agreement [Member]	Dec. 31, 2011 AA Bank of America Agreement [Member]	Jun. 30, 2012 A	Dec. 31, 2011 A	Jun. 30, 2012 BBB	Dec. 31, 2011 BBB	Jun. 30, 2012 Below investment grade ("BIG")	Dec. 31, 2011 Below investment grade ("BIG")	Jun. 30, 2012 US Public Finance [Member]	Dec. 31, 2011 US Public Finance [Member]	Jun. 30, 2012 US Public Finance [Member] Super senior	Dec. 31, 2011 US Public Finance [Member] Super senior	Jun. 30, 2012 US Public Finance [Member] AAA	Dec. 31, 2011 US Public Finance [Member] AAA	Jun. 30, 2012 US Public Finance [Member] AA	Dec. 31, 2011 US Public Finance [Member] AA	Jun. 30, 2012 US Public Finance [Member] A	Dec. 31, 2011 US Public Finance [Member] A	Jun. 30, 2012 US Public Finance [Member] BBB	Dec. 31, 2011 US Public Finance [Member] BBB	Jun. 30, 2012 US Public Finance [Member] Below investment grade ("BIG")	Dec. 31, 2011 US Public Finance [Member] Below investment grade ("BIG")	Jun. 30, 2012 Public finance Non-U.S.		Dec. 31, 2011 Public finance Non-U.S.		Jun. 30, 2012 Public finance Non-U.S. Super senior	Dec. 31, 2011 Public finance Non-U.S. Super senior	Jun. 30, 2012 Public finance Non-U.S. AAA	Dec. 31, 2011 Public finance Non-U.S. AAA	Jun. 30, 2012 Public finance Non-U.S. AA	Dec. 31, 2011 Public finance Non-U.S. AA	Jun. 30, 2012 Public finance Non-U.S. A	Dec. 31, 2011 Public finance Non-U.S. A	Jun. 30, 2012 Public finance Non-U.S. BBB	Dec. 31, 2011 Public finance Non-U.S. BBB	Jun. 30, 2012 Public finance Non-U.S. Below investment grade ("BIG")		Dec. 31, 2011 Public finance Non-U.S. Below investment grade ("BIG")		Jun. 30, 2012 Structured finance U.S.	Dec. 31, 2011 Structured finance U.S.	Jun. 30, 2012 Structured finance U.S. Super senior	Dec. 31, 2011 Structured finance U.S. Super senior	Jun. 30, 2012 Structured finance U.S. AAA	Dec. 31, 2011 Structured finance U.S. AAA	Jun. 30, 2012 Structured finance U.S. AA	Dec. 31, 2011 Structured finance U.S. AA	Jun. 30, 2012 Structured finance U.S. A	Dec. 31, 2011 Structured finance U.S. A	Jun. 30, 2012 Structured finance U.S. BBB	Dec. 31, 2011 Structured finance U.S. BBB	Jun. 30, 2012 Structured finance U.S. Below investment grade ("BIG")	Dec. 31, 2011 Structured finance U.S. Below investment grade ("BIG")	Jun. 30, 2012 Structured finance Non-U.S.	Dec. 31, 2011 Structured finance Non-U.S.	Jun. 30, 2012 Structured finance Non-U.S. Super senior	Dec. 31, 2011 Structured finance Non-U.S. Super senior	Jun. 30, 2012 Structured finance Non-U.S. AAA	Dec. 31, 2011 Structured finance Non-U.S. AAA	Jun. 30, 2012 Structured finance Non-U.S. AA	Dec. 31, 2011 Structured finance Non-U.S. AA	Jun. 30, 2012 Structured finance Non-U.S. A	Dec. 31, 2011 Structured finance Non-U.S. A	Jun. 30, 2012 Structured finance Non-U.S. BBB	Dec. 31, 2011 Structured finance Non-U.S. BBB	Jun. 30, 2012 Structured finance Non-U.S. Below investment grade ("BIG")	Dec. 31, 2011 Structured finance Non-U.S. Below investment grade ("BIG")	Jun. 30, 2012 Public finance UK	Jun. 30, 2012 Public finance Ireland	Jun. 30, 2012 Structured finance	Jun. 30, 2012 Public finance	Jun. 30, 2012 Public finance Minimum	Jun. 30, 2012 Public finance Maximum
Outstanding Exposure
Net mortgage guaranty insurance in force	$ 148,000,000																																																																												$ 15,000,000	$ 133,000,000
Net Par Amount Outstanding	552,934,000,000	558,048,000,000	21,043,000,000	23,554,000,000	48,331,000,000	52,422,000,000	149,012,000,000	154,300,000,000			236,855,000,000	230,541,000,000	72,879,000,000	70,469,000,000	24,814,000,000	26,762,000,000	409,877,000,000	403,073,000,000	0	0	4,771,000,000	5,074,000,000	136,709,000,000	139,693,000,000	220,154,000,000	213,164,000,000	43,836,000,000	40,635,000,000	4,407,000,000	4,507,000,000	38,769,000,000	[1]	39,046,000,000	[1]	1,109,000,000	1,138,000,000	1,388,000,000	1,381,000,000	998,000,000	1,056,000,000	10,657,000,000	11,744,000,000	22,102,000,000	21,399,000,000	2,515,000,000	[1]	2,328,000,000	[1]	83,430,000,000	92,234,000,000	15,157,000,000	16,756,000,000	32,947,000,000	35,736,000,000	10,416,000,000	12,575,000,000	4,692,000,000	4,115,000,000	4,201,000,000	5,044,000,000	16,017,000,000	18,008,000,000	20,858,000,000	23,695,000,000	4,777,000,000	5,660,000,000	9,225,000,000	10,231,000,000	889,000,000	976,000,000	1,352,000,000	1,518,000,000	2,740,000,000	3,391,000,000	1,875,000,000	1,919,000,000
% of Total Net Par Outstanding	100.00%	100.00%	3.80%	4.20%	8.70%	9.40%	27.00%	27.70%			42.80%	41.30%	13.20%	12.60%	4.50%	4.80%	100.00%	100.00%	0.00%	0.00%	1.20%	1.30%	33.30%	34.60%	53.70%	52.90%	10.70%	10.10%	1.10%	1.10%	100.00%		100.00%		2.80%	2.90%	3.60%	3.50%	2.60%	2.70%	27.50%	30.10%	57.00%	54.80%	6.50%		6.00%		100.00%	100.00%	18.20%	18.20%	39.50%	38.70%	12.50%	13.60%	5.60%	4.50%	5.00%	5.50%	19.20%	19.50%	100.00%	100.00%	22.90%	23.90%	44.20%	43.20%	4.30%	4.10%	6.50%	6.40%	13.10%	14.30%	9.00%	8.10%
Percentage of the first lien transactions covered by the Bank of America Agreement reclassified to AA									80.00%
Decrease of net outstanding par rated of the first lien transactions covered by the Bank of America Agreement reclassified to AA										1,452,000,000
Outstanding commitments to provide guaranties																																																																															1,800,000,000	500,000,000
Expiration date for insured financial obligation commitments																																																																																	Jul. 01, 2012	Feb. 25, 2017
Outstanding commitments to provide guaranties, amount expiring prior to December 31, 2012																																																																																$ 200,000,000

[1] Includes $276 million and $282 million in net par as of June 30, 2012 and December 31, 2011, respectively, for bonds of the Hellenic Republic of Greece, a portion of which was accelerated in July 2012 and a portion of which the Company intends to accelerate on or after September 2012. See Note 4, Financial Guaranty Insurance Contracts.