Subsidiary Information - Condensed Consolidating Balance Sheet (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Assets
Total investment portfolio and cash	$ 11,459	$ 10,969
Investment in subsidiaries	0	0
Premiums receivable, net of commissions payable	729	876
Ceded unearned premium reserve	381	452
Deferred acquisition costs	121	124	116	132
Reinsurance recoverable on unpaid losses	78	36
Credit derivative assets	68	94
Deferred tax asset, net	260	688
Intercompany receivable	0	0
Financial guaranty variable interest entities’ assets, at fair value	1,402	2,565
Other	427	483
Total assets	14,925	16,287
Liabilities and shareholders’ equity
Unearned premium reserve	4,261	4,595
Loss and loss adjustment expense reserve	799	592
Long-term debt	1,303	816
Intercompany payable	0	0
Credit derivative liabilities	963	1,787
Deferred tax liabilities, net	0	0
Financial guaranty variable interest entities’ liabilities, at fair value	1,419	2,871
Other	422	511
Total liabilities	9,167	11,172
Effect on shareholders’ equity (decrease) increase	5,758	5,115	4,994	4,652
Noncontrolling interest	0	0
Total shareholders' equity	5,758	5,115
Total liabilities and shareholders’ equity	14,925	16,287
Reportable Legal Entities [Member] | Assured Guaranty Ltd. (Parent) [Member]
Assets
Total investment portfolio and cash	126	33
Investment in subsidiaries	5,612	5,066
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	27	23
Total assets	5,765	5,122
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	7	7
Total liabilities	7	7
Effect on shareholders’ equity (decrease) increase	5,758	5,115
Noncontrolling interest	0	0
Total shareholders' equity	5,758	5,115
Total liabilities and shareholders’ equity	5,765	5,122
Reportable Legal Entities [Member] | AGUS (Issuer) [Member]
Assets
Total investment portfolio and cash	204	186
Investment in subsidiaries	5,072	4,191
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	54	97
Intercompany receivable	0	0
Financial guaranty variable interest entities’ assets, at fair value	0	0
Other	77	17
Total assets	5,407	4,491
Liabilities and shareholders’ equity
Unearned premium reserve	0	0
Loss and loss adjustment expense reserve	0	0
Long-term debt	847	348
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	9	7
Total liabilities	946	445
Effect on shareholders’ equity (decrease) increase	4,461	4,046
Noncontrolling interest	0	0
Total shareholders' equity	4,461	4,046
Total liabilities and shareholders’ equity	5,407	4,491
Reportable Legal Entities [Member] | AGMH (Issuer) [Member]
Assets
Total investment portfolio and cash	47	42
Investment in subsidiaries	3,965	3,574
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	27	31
Total assets	4,039	3,647
Liabilities and shareholders’ equity
Unearned premium reserve	0	0
Loss and loss adjustment expense reserve	0	0
Long-term debt	437	430
Intercompany payable	0	0
Credit derivative liabilities	0	0
Deferred tax liabilities, net	94	95
Financial guaranty variable interest entities’ liabilities, at fair value	0	0
Other	16	16
Total liabilities	547	541
Effect on shareholders’ equity (decrease) increase	3,492	3,106
Noncontrolling interest	0	0
Total shareholders' equity	3,492	3,106
Total liabilities and shareholders’ equity	4,039	3,647
Reportable Legal Entities [Member] | Other Entities [Member]
Assets
Total investment portfolio and cash	11,382	11,008
Investment in subsidiaries	339	289
Premiums receivable, net of commissions payable	864	1,025
Ceded unearned premium reserve	1,469	1,598
Deferred acquisition costs	186	198
Reinsurance recoverable on unpaid losses	338	170
Credit derivative assets	277	482
Deferred tax asset, net	295	681
Intercompany receivable	90	90
Financial guaranty variable interest entities’ assets, at fair value	1,402	2,565
Other	538	638
Total assets	17,180	18,744
Liabilities and shareholders’ equity
Unearned premium reserve	5,328	5,720
Loss and loss adjustment expense reserve	1,066	733
Long-term debt	19	38
Intercompany payable	300	300
Credit derivative liabilities	1,172	2,175
Deferred tax liabilities, net	0	0
Financial guaranty variable interest entities’ liabilities, at fair value	1,419	2,871
Other	764	853
Total liabilities	10,068	12,690
Effect on shareholders’ equity (decrease) increase	6,773	5,765
Noncontrolling interest	339	289
Total shareholders' equity	7,112	6,054
Total liabilities and shareholders’ equity	17,180	18,744
Consolidating Adjustments [Member]
Assets
Total investment portfolio and cash	(300)	(300)
Investment in subsidiaries	(14,988)	(13,120)
Premiums receivable, net of commissions payable	(135)	(149)
Ceded unearned premium reserve	(1,088)	(1,146)
Deferred acquisition costs	(65)	(74)
Reinsurance recoverable on unpaid losses	(260)	(134)
Credit derivative assets	(209)	(388)
Deferred tax asset, net	(89)	(90)
Intercompany receivable	(90)	(90)
Financial guaranty variable interest entities’ assets, at fair value	0	0
Other	(242)	(226)
Total assets	(17,466)	(15,717)
Liabilities and shareholders’ equity
Unearned premium reserve	(1,067)	(1,125)
Loss and loss adjustment expense reserve	(267)	(141)
Long-term debt	0	0
Intercompany payable	(390)	(390)
Credit derivative liabilities	(209)	(388)
Deferred tax liabilities, net	(94)	(95)
Financial guaranty variable interest entities’ liabilities, at fair value	0	0
Other	(374)	(372)
Total liabilities	(2,401)	(2,511)
Effect on shareholders’ equity (decrease) increase	(14,726)	(12,917)
Noncontrolling interest	(339)	(289)
Total shareholders' equity	(15,065)	(13,206)
Total liabilities and shareholders’ equity	$ (17,466)	$ (15,717)