Insurance Company Regulatory Requirements - Insurance Regulatory Amounts Reported (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
AGM [Member]
Statutory Accounting Practices [Line Items]
Policyholders' surplus	$ 2,691	$ 2,533
Net Income (Loss)	312	172	$ 152
Statutory Accounting Practices, Statutory Capital and Surplus Required	869	913
AGC [Member]
Statutory Accounting Practices [Line Items]
Policyholders' surplus	1,775	1,793
Net Income (Loss)	226	(5)	219
Statutory Accounting Practices, Statutory Capital and Surplus Required	546	550
MAC [Member]
Statutory Accounting Practices [Line Items]
Policyholders' surplus	276	321
Net Income (Loss)	53	55	32
Statutory Accounting Practices, Statutory Capital and Surplus Required	192	200
Assured Guaranty Re [Member]
Statutory Accounting Practices [Line Items]
Policyholders' surplus	1,098	1,249
Net Income (Loss)	45	131	155
Assured Guaranty Re Overseas [Member]
Statutory Accounting Practices [Line Items]
Policyholders' surplus	410	383
Net Income (Loss)	$ 12	$ 10	$ 10
Subsidiaries [Member] | AGM [Member] | Municipal Assurance Corp Holdings [Member]
Statutory Accounting Practices [Line Items]
Holding company's percent ownership of common stock	60.70%
Subsidiaries [Member] | AGC [Member] | Municipal Assurance Corp Holdings [Member]
Statutory Accounting Practices [Line Items]
Holding company's percent ownership of common stock	39.30%
Subsidiaries [Member] | MAC [Member] | Municipal Assurance Corp Holdings [Member]
Statutory Accounting Practices [Line Items]
Holding company's percent ownership of common stock	100.00%