Insurance Company Regulatory Requirements - Insurance Regulatory Amounts Reported (Details) - USD ($)		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Apr. 01, 2015	Jul. 17, 2013	Jul. 16, 2013
Municipal Assurance Corp Holdings [Member]
Statutory Accounting Practices [Line Items]
Policyholders' surplus						$ 400,000,000
AGM [Member]
Statutory Accounting Practices [Line Items]
Policyholders' surplus	[1]	$ 2,441,000,000	$ 2,267,000,000
Net Income (Loss)	[1]	217,000,000	304,000,000	$ 340,000,000
MAC [Member]
Statutory Accounting Practices [Line Items]
Policyholders' surplus		730,000,000	612,000,000				$ 800,000,000
Net Income (Loss)		102,000,000	75,000,000	26,000,000
AGC [Member]
Statutory Accounting Practices [Line Items]
Policyholders' surplus	[1],[2]	1,365,000,000	1,086,000,000
Net Income (Loss)	[1],[2]	(92,000,000)	116,000,000	211,000,000
Assured Guaranty Re [Member]
Statutory Accounting Practices [Line Items]
Policyholders' surplus		1,018,000,000	1,114,000,000
Net Income (Loss)		$ 85,000,000	$ 28,000,000	$ 103,000,000
Subsidiaries [Member] | AGM [Member] | Municipal Assurance Corp Holdings [Member]
Statutory Accounting Practices [Line Items]
Holding company's percent ownership of common stock						61.00%
Subsidiaries [Member] | MAC [Member] | Municipal Assurance Corp Holdings [Member]
Statutory Accounting Practices [Line Items]
Holding company's percent ownership of common stock						100.00%
Subsidiaries [Member] | AGC [Member] | Municipal Assurance Corp Holdings [Member]
Statutory Accounting Practices [Line Items]
Holding company's percent ownership of common stock						39.00%
Radian [Member] | AGC [Member]
Statutory Accounting Practices [Line Items]
Policyholders' surplus	[1]				$ 333,000,000

[1] Policyholders' surplus of AGM and AGC include their indirect share of MAC. AGM and AGC own approximately 61% and 39%, respectively, of the outstanding stock of Municipal Assurance Holdings Inc. ("MAC Holdings"), which owns 100% of the outstanding common stock of MAC.

[2] As indicated in Note 2, Acquisition of Radian Asset Assurance Inc., AGC completed the acquisition of Radian Asset on April 1, 2015. Radian Asset was merged with and into AGC, with AGC as the surviving company of the merger. The impact to AGC's policyholders' surplus was approximately $333 million, on a statutory basis, as of April 1, 2015.