Subsidiary Information - Condensed Consolidating Balance Sheet (Details) - USD ($) $ in Millions	Sep. 30, 2015		Dec. 31, 2014
Assets
Total investment portfolio and cash	$ 11,409		$ 11,459
Investment in subsidiaries	0		0
Premiums receivable, net of commissions payable	676		729
Ceded unearned premium reserve	263		381
Deferred acquisition costs	118		121
Reinsurance recoverable on unpaid losses	89		78
Credit derivative assets	71		68
Deferred tax asset, net	426		260
Intercompany receivable	0		0
Financial guaranty variable interest entities’ assets, at fair value	1,547	[1]	1,402
Other	435		427
Total assets	15,034		14,925
Liabilities and shareholders’ equity
Unearned premium reserve	4,112		4,261
Loss and loss adjustment expense reserve	1,007		799
Long-term debt	1,306		1,303
Intercompany payable	0		0
Credit derivative liabilities	918		963
Deferred tax liabilities, net	0		0
Financial guaranty variable interest entities’ liabilities, at fair value	1,482	[1]	1,419
Other	390		422
Total liabilities	9,215		9,167
Effect on shareholders’ equity (decrease) increase	5,819		5,758
Noncontrolling interest	0		0
Total shareholders' equity	5,819		5,758
Total liabilities and shareholders’ equity	15,034		14,925
Reportable Legal Entities [Member] | Assured Guaranty Ltd. (Parent) [Member]
Assets
Total investment portfolio and cash	100		126
Investment in subsidiaries	5,696		5,612
Premiums receivable, net of commissions payable	0		0
Ceded unearned premium reserve	0		0
Deferred acquisition costs	0		0
Reinsurance recoverable on unpaid losses	0		0
Credit derivative assets	0		0
Deferred tax asset, net	0		0
Intercompany receivable	0		0
Financial guaranty variable interest entities’ assets, at fair value	0		0
Other	28		27
Total assets	5,824		5,765
Liabilities and shareholders’ equity
Unearned premium reserve	0		0
Loss and loss adjustment expense reserve	0		0
Long-term debt	0		0
Intercompany payable	0		0
Credit derivative liabilities	0		0
Deferred tax liabilities, net	0		0
Financial guaranty variable interest entities’ liabilities, at fair value	0		0
Other	5		7
Total liabilities	5		7
Effect on shareholders’ equity (decrease) increase	5,819		5,758
Noncontrolling interest	0		0
Total shareholders' equity	5,819		5,758
Total liabilities and shareholders’ equity	5,824		5,765
Reportable Legal Entities [Member] | AGUS (Issuer) [Member]
Assets
Total investment portfolio and cash	61		204
Investment in subsidiaries	5,348		5,072
Premiums receivable, net of commissions payable	0		0
Ceded unearned premium reserve	0		0
Deferred acquisition costs	0		0
Reinsurance recoverable on unpaid losses	0		0
Credit derivative assets	0		0
Deferred tax asset, net	37		54
Intercompany receivable	0		0
Financial guaranty variable interest entities’ assets, at fair value	0		0
Other	107		77
Total assets	5,553		5,407
Liabilities and shareholders’ equity
Unearned premium reserve	0		0
Loss and loss adjustment expense reserve	0		0
Long-term debt	847		847
Intercompany payable	90		90
Credit derivative liabilities	0		0
Deferred tax liabilities, net	0		0
Financial guaranty variable interest entities’ liabilities, at fair value	0		0
Other	24		9
Total liabilities	961		946
Effect on shareholders’ equity (decrease) increase	4,592		4,461
Noncontrolling interest	0		0
Total shareholders' equity	4,592		4,461
Total liabilities and shareholders’ equity	5,553		5,407
Reportable Legal Entities [Member] | AGMH (Issuer) [Member]
Assets
Total investment portfolio and cash	22		47
Investment in subsidiaries	4,042		3,965
Premiums receivable, net of commissions payable	0		0
Ceded unearned premium reserve	0		0
Deferred acquisition costs	0		0
Reinsurance recoverable on unpaid losses	0		0
Credit derivative assets	0		0
Deferred tax asset, net	0		0
Intercompany receivable	0		0
Financial guaranty variable interest entities’ assets, at fair value	0		0
Other	39		27
Total assets	4,103		4,039
Liabilities and shareholders’ equity
Unearned premium reserve	0		0
Loss and loss adjustment expense reserve	0		0
Long-term debt	444		437
Intercompany payable	0		0
Credit derivative liabilities	0		0
Deferred tax liabilities, net	91		94
Financial guaranty variable interest entities’ liabilities, at fair value	0		0
Other	20		16
Total liabilities	555		547
Effect on shareholders’ equity (decrease) increase	3,548		3,492
Noncontrolling interest	0		0
Total shareholders' equity	3,548		3,492
Total liabilities and shareholders’ equity	4,103		4,039
Reportable Legal Entities [Member] | Other Entities [Member]
Assets
Total investment portfolio and cash	11,595		11,382
Investment in subsidiaries	369		339
Premiums receivable, net of commissions payable	814		864
Ceded unearned premium reserve	1,316		1,469
Deferred acquisition costs	182		186
Reinsurance recoverable on unpaid losses	461		338
Credit derivative assets	249		277
Deferred tax asset, net	517		295
Intercompany receivable	90		90
Financial guaranty variable interest entities’ assets, at fair value	1,547		1,402
Other	599		538
Total assets	17,739		17,180
Liabilities and shareholders’ equity
Unearned premium reserve	5,285		5,328
Loss and loss adjustment expense reserve	1,438		1,066
Long-term debt	15		19
Intercompany payable	300		300
Credit derivative liabilities	1,096		1,172
Deferred tax liabilities, net	0		0
Financial guaranty variable interest entities’ liabilities, at fair value	1,482		1,419
Other	816		764
Total liabilities	10,432		10,068
Effect on shareholders’ equity (decrease) increase	6,938		6,773
Noncontrolling interest	369		339
Total shareholders' equity	7,307		7,112
Total liabilities and shareholders’ equity	17,739		17,180
Consolidating Adjustments [Member]
Assets
Total investment portfolio and cash	(369)		(300)
Investment in subsidiaries	(15,455)		(14,988)
Premiums receivable, net of commissions payable	(138)		(135)
Ceded unearned premium reserve	(1,053)		(1,088)
Deferred acquisition costs	(64)		(65)
Reinsurance recoverable on unpaid losses	(372)		(260)
Credit derivative assets	(178)		(209)
Deferred tax asset, net	(128)		(89)
Intercompany receivable	(90)		(90)
Financial guaranty variable interest entities’ assets, at fair value	0		0
Other	(338)		(242)
Total assets	(18,185)		(17,466)
Liabilities and shareholders’ equity
Unearned premium reserve	(1,173)		(1,067)
Loss and loss adjustment expense reserve	(431)		(267)
Long-term debt	0		0
Intercompany payable	(390)		(390)
Credit derivative liabilities	(178)		(209)
Deferred tax liabilities, net	(91)		(94)
Financial guaranty variable interest entities’ liabilities, at fair value	0		0
Other	(475)		(374)
Total liabilities	(2,738)		(2,401)
Effect on shareholders’ equity (decrease) increase	(15,078)		(14,726)
Noncontrolling interest	(369)		(339)
Total shareholders' equity	(15,447)		(15,065)
Total liabilities and shareholders’ equity	$ (18,185)		$ (17,466)

[1] The September 30, 2015 amounts include $115 million of FG VIE assets and $111 million of FG VIE liabilities acquired from Radian Asset.