Insurance Company Regulatory Requirements - Dividends and Surplus Notes By Insurance Company Subsidiaries (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Statutory Accounting Practices [Line Items]
Dividends paid	$ 19	$ 18
Municipal Assurance Corp Holdings [Member] | Affiliated Entity [Member] | Municipal Assurance Corp [Member]
Statutory Accounting Practices [Line Items]
Dividends paid	12	0
AGMH [Member] | Affiliated Entity [Member] | AGM [Member]
Statutory Accounting Practices [Line Items]
Dividends paid	79	95
AGL [Member] | Affiliated Entity [Member] | Assured Guaranty Re [Member]
Statutory Accounting Practices [Line Items]
Dividends paid	40	25
AGUS [Member] | Affiliated Entity [Member] | AGC [Member]
Statutory Accounting Practices [Line Items]
Dividends paid	$ 28	$ 0