Insurance Company Regulatory Requirements - Insurance Regulatory Amounts Reported (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jul. 17, 2013
AGM [Member]
Statutory Accounting Practices [Line Items]
Policyholders' surplus	$ 2,533	$ 2,254
Net Income (Loss)	172	152	$ 191
Statutory Accounting Practices, Statutory Capital and Surplus Required	913	972
MAC [Member]
Statutory Accounting Practices [Line Items]
Policyholders' surplus	321	270
Net Income (Loss)	55	32	142
Statutory Accounting Practices, Statutory Capital and Surplus Required	200	224
AGC [Member]
Statutory Accounting Practices [Line Items]
Policyholders' surplus	1,793	2,073
Net Income (Loss)	(5)	219	108
Statutory Accounting Practices, Statutory Capital and Surplus Required	550	554
Assured Guaranty Re [Member]
Statutory Accounting Practices [Line Items]
Policyholders' surplus	1,249	1,294
Net Income (Loss)	131	155	139
Assured Guaranty Re Overseas [Member]
Statutory Accounting Practices [Line Items]
Policyholders' surplus	383	380
Net Income (Loss)	$ 10	$ 10	$ 8
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%