Insurance Company Regulatory Requirements - Dividends and Surplus Notes By Insurance Company Subsidiaries (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Statutory Accounting Practices [Line Items]
Dividends paid				$ 35	$ 37
AGM and AGC [Member] | Affiliated Entity [Member] | Municipal Assurance Corp Holdings [Member]
Statutory Accounting Practices [Line Items]
Distribution to owners		$ 300
Municipal Assurance Corp Holdings [Member] | Affiliated Entity [Member] | Municipal Assurance Corp [Member]
Statutory Accounting Practices [Line Items]
Repayment of surplus notes	[1]	300	$ 0	300	0
AGM [Member] | Affiliated Entity [Member] | Municipal Assurance Corp [Member]
Statutory Accounting Practices [Line Items]
Repayment of surplus notes		100	0	100	0
AGMH [Member] | Affiliated Entity [Member] | AGM [Member]
Statutory Accounting Practices [Line Items]
Dividends paid		32	40	127	106
Repayment of surplus notes		0	0	0	25
AGL [Member] | Affiliated Entity [Member] | Assured Guaranty Re [Member]
Statutory Accounting Practices [Line Items]
Dividends paid		25	35	50	85
AGUS [Member] | Affiliated Entity [Member] | AGC [Member]
Statutory Accounting Practices [Line Items]
Dividends paid		$ 23	$ 15	$ 23	$ 35

[1] MAC Holdings returned $300 million to AGM and AGC, in proportion to their ownership percentages, in Second Quarter 2016.