Insurance Company Regulatory Requirements (Details) (USD $)	3 Months Ended		12 Months Ended						3 Months Ended	12 Months Ended				12 Months Ended																				12 Months Ended						3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended
	Sep. 30, 2013	Dec. 31, 2013	Dec. 31, 2013 AGC	Dec. 31, 2012 AGC	Dec. 31, 2011 AGC	Dec. 31, 2013 AGC Maryland	Dec. 31, 2012 AGC Maryland	Dec. 31, 2011 AGC Maryland	Sep. 30, 2013 AGM	Dec. 31, 2013 AGM	Dec. 31, 2012 AGM	Dec. 31, 2011 AGM	Jul. 16, 2013 AGM	Dec. 31, 2013 AGM New York	Dec. 31, 2012 AGM New York	Dec. 31, 2011 AGM New York	Dec. 31, 2013 Assured Guaranty Municipal Insurance Company [Member]	Dec. 31, 2012 Assured Guaranty Municipal Insurance Company [Member]	Dec. 31, 2011 Assured Guaranty Municipal Insurance Company [Member]	Dec. 31, 2013 AGM Consolidated [Member]		Dec. 31, 2012 AGM Consolidated [Member]		Dec. 31, 2011 AGM Consolidated [Member]		Dec. 31, 2013 AG Re	Dec. 31, 2012 AG Re	Dec. 31, 2011 AG Re	Dec. 31, 2013 AG Re Bermuda	Dec. 31, 2012 AG Re Bermuda	Dec. 31, 2011 AG Re Bermuda	Dec. 31, 2013 AG Re Minimum Bermuda	Dec. 31, 2013 AG Re Maximum Bermuda	Dec. 31, 2013 MAC	Dec. 31, 2012 MAC	Dec. 31, 2011 MAC	Jul. 16, 2013 MAC	Jul. 16, 2013 AGBM	Jul. 16, 2013 MAC Holdings	Sep. 30, 2013 AGC	Dec. 31, 2013 AGC	Sep. 30, 2013 AGC Maryland	Dec. 31, 2013 AGC Maryland	Sep. 30, 2013 AGM and AGE New York	Sep. 30, 2013 AGM and AGC
Insurance company regulatory requirements
Payments of Dividends						$ 67,000,000	$ 55,000,000	$ 30,000,000						$ 163,000,000	$ 30,000,000	$ 0													$ 144,000,000	$ 151,000,000	$ 86,000,000
Rate at which present value of expected losses are discounted (as a percent)		5.00%
Policyholders' Surplus			693,000,000	905,000,000						1,733,000,000	1,780,000,000						0	791,000,000		1,746,000,000	[1]	1,785,000,000	[1]			1,122,000,000	1,283,000,000		600,000,000					514,000,000	77,000,000		800,000,000
Net Income (Loss)			211,000,000	31,000,000	230,000,000					340,000,000	203,000,000	399,000,000					0	58,000,000	197,000,000	405,000,000	[1]	256,000,000	[1]	632,000,000	[1]	107,000,000	117,000,000	133,000,000						26,000,000	1,000,000	0
Intercompany loan													100,000,000																									82,500,000	300,000,000
Holding company's percent ownership of common stock																																							100.00%
Subsidiary percent ownership of common stock			39.00%							61.00%																															39.00%
Payments for interest in subsidiary									425,000,000																															275,000,000
Statutory surplus, balance																																					400,000,000
Intercompany, ceded premiums									87,000,000,000																															24,000,000,000
Intercompany, ceded unearned premiums									468,000,000																															249,000,000
Contingency reserves reassumed, remainder of fiscal year, percent																																										33.00%		33.00%	33.00%
Contingency reserves reassumed, release of assets	130,000,000
Contingency reserves reassumed, remainder of fiscal year, amount																																										267,000,000		250,000,000
Contingency reserves reassumed, year two, percentage																																										50.00%		50.00%
Contingency reserves reassumed, year three, percentage																																										17.00%		17.00%
Threshold for dividend payments as a percentage of policyholder surplus						10.00%								10.00%																													10.00%
Threshold for dividend payments, percentage of adjusted net investment income						100.00%								100.00%																													100.00%
Amount available for distribution, current year						2,000,000								10,000,000															281,000,000
Amount available for distribution, 2014						69,000,000								173,000,000
Period in which no dividends would be paid														2 years
Unencumbered assets																													238,000,000
Dividend restrictions on outstanding statutory surplus																																	278,000,000
Dividend restrictions on statutory capital and surplus (as a percent)																																25.00%
Period for filing affidavit prior to dividend payment (in days)																													7 days
Dividend restrictions on statutory capital (as a percent)																													15.00%
Dividend restrictions on statutory capital																														126,000,000
Relevant assets as a percentage of relevant liabilities																																75.00%
Repayment of surplus note										50,000,000	50,000,000	50,000,000
Issuance of surplus notes																																		$ (400,000,000)	$ 0	$ 0

[1] Represents the consolidated amounts of AGM and all of its U.S. and foreign subsidiaries.