Insurance Company Regulatory Requirements - Insurance Regulatory Amounts Reported (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012		Jul. 16, 2013
AGM [Member]
Statutory Accounting Practices [Line Items]
Policyholders' surplus	$ 2,267	[1]	$ 1,733	[1]
Net Income (Loss)	304	[1]	340	[1]	203	[1]
MAC [Member]
Statutory Accounting Practices [Line Items]
Policyholders' surplus	612		514				800
Net Income (Loss)	75		26		1
AGC [Member]
Statutory Accounting Practices [Line Items]
Policyholders' surplus	1,086	[1]	693	[1]
Net Income (Loss)	116	[1]	211	[1]	31	[1]
Assured Guaranty Re [Member]
Statutory Accounting Practices [Line Items]
Policyholders' surplus	1,114		1,119
Net Income (Loss)	$ 28		$ 103		$ 117

[1] Policyholders' surplus of AGM and AGC include their indirect share of MAC. AGM and AGC own approximately 61% and 39%, respectively, of the outstanding stock of Municipal Assurance Holdings Inc. ("MAC Holdings"), which owns 100% of the outstanding common stock of MAC.