Insurance Company Regulatory Requirements - Dividends and Surplus Notes By Insurance Company Subsidiaries (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Statutory Accounting Practices [Line Items]
Dividends paid			$ 36	$ 35
Municipal Assurance Corp Holdings [Member] | Affiliated Entity [Member] | Municipal Assurance Corp [Member]
Statutory Accounting Practices [Line Items]
Dividends paid	$ 12	$ 0	24	0
Statutory Accounting Practices, Intercompany Transaction, Repayment of Surplus Notes	0	300	0	300
AGM [Member] | Affiliated Entity [Member] | Municipal Assurance Corp [Member]
Statutory Accounting Practices [Line Items]
Statutory Accounting Practices, Intercompany Transaction, Repayment of Surplus Notes	0	100	0	100
AGMH [Member] | Affiliated Entity [Member] | AGM [Member]
Statutory Accounting Practices [Line Items]
Dividends paid	0	32	79	127
AGL [Member] | Affiliated Entity [Member] | Assured Guaranty Re [Member]
Statutory Accounting Practices [Line Items]
Dividends paid	40	25	80	50
AGUS [Member] | Affiliated Entity [Member] | AGC [Member]
Statutory Accounting Practices [Line Items]
Dividends paid	$ 23	$ 23	$ 51	$ 23