Subsidiary Information - Condensed Consolidating Balance Sheet (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Assets
Total investment portfolio and cash	$ 11,488	$ 11,103
Investment in subsidiaries	0	0
Premiums receivable, net of commissions payable	876	576
Ceded unearned premium reserve	180	206
Deferred acquisition costs	106	106
Reinsurance recoverable on unpaid losses	74	80
Credit derivative assets	9	13
Deferred tax asset, net	438	497
Intercompany receivable	0	0
Financial guaranty variable interest entities’ assets, at fair value	781	876
Dividend receivable from affiliate	0	0
Other	723	694
Total assets	14,675	14,151
Liabilities and shareholders’ equity
Unearned premium reserve	3,827	3,511
Loss and loss adjustment expense reserve	1,193	1,127
Long-term debt	1,307	1,306
Intercompany payable	0	0
Credit derivative liabilities	359	402
Deferred tax liabilities, net	0	0
Financial guaranty variable interest entities’ liabilities, at fair value	855	958
Dividend payable to affiliate	0	0
Other	497	343
Total liabilities	8,038	7,647
Effect on shareholders' equity (decrease) increase	6,637	6,504
Noncontrolling interest	0	0
Total shareholders' equity	6,637	6,504
Total liabilities and shareholders’ equity	14,675	14,151
Reportable Legal Entities [Member] | Assured Guaranty Ltd. (Parent) [Member]
Assets
Total investment portfolio and cash	12	36
Investment in subsidiaries	6,504	6,164
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
Dividend receivable from affiliate	125	300
Other	0	11
Total assets	6,641	6,511
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
Dividend payable to affiliate	0	0
Other	4	7
Total liabilities	4	7
Effect on shareholders' equity (decrease) increase	6,637	6,504
Noncontrolling interest	0	0
Total shareholders' equity	6,637	6,504
Total liabilities and shareholders’ equity	6,641	6,511
Reportable Legal Entities [Member] | AGUS (Issuer) [Member]
Assets
Total investment portfolio and cash	312	384
Investment in subsidiaries	5,852	5,696
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	16
Intercompany receivable	0	0
Financial guaranty variable interest entities’ assets, at fair value	0	0
Dividend receivable from affiliate	0	0
Other	97	78
Total assets	6,261	6,174
Liabilities and shareholders’ equity
Unearned premium reserve	0	0
Loss and loss adjustment expense reserve	0	0
Long-term debt	843	843
Intercompany payable	70	70
Credit derivative liabilities	0	0
Deferred tax liabilities, net	1	0
Financial guaranty variable interest entities’ liabilities, at fair value	0	0
Dividend payable to affiliate	125	300
Other	20	3
Total liabilities	1,059	1,216
Effect on shareholders' equity (decrease) increase	5,202	4,958
Noncontrolling interest	0	0
Total shareholders' equity	5,202	4,958
Total liabilities and shareholders’ equity	6,261	6,174
Reportable Legal Entities [Member] | AGMH (Issuer) [Member]
Assets
Total investment portfolio and cash	20	22
Investment in subsidiaries	3,805	3,734
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
Dividend receivable from affiliate	0	0
Other	38	26
Total assets	3,863	3,782
Liabilities and shareholders’ equity
Unearned premium reserve	0	0
Loss and loss adjustment expense reserve	0	0
Long-term debt	455	453
Intercompany payable	0	0
Credit derivative liabilities	0	0
Deferred tax liabilities, net	87	88
Financial guaranty variable interest entities’ liabilities, at fair value	0	0
Dividend payable to affiliate	0	0
Other	26	14
Total liabilities	568	555
Effect on shareholders' equity (decrease) increase	3,295	3,227
Noncontrolling interest	0	0
Total shareholders' equity	3,295	3,227
Total liabilities and shareholders’ equity	3,863	3,782
Reportable Legal Entities [Member] | Other Entities [Member]
Assets
Total investment portfolio and cash	11,503	11,029
Investment in subsidiaries	299	296
Premiums receivable, net of commissions payable	1,008	699
Ceded unearned premium reserve	1,074	1,099
Deferred acquisition costs	155	156
Reinsurance recoverable on unpaid losses	383	484
Credit derivative assets	53	69
Deferred tax asset, net	540	597
Intercompany receivable	70	70
Financial guaranty variable interest entities’ assets, at fair value	781	876
Dividend receivable from affiliate	0	0
Other	835	801
Total assets	16,701	16,176
Liabilities and shareholders’ equity
Unearned premium reserve	4,800	4,488
Loss and loss adjustment expense reserve	1,491	1,596
Long-term debt	9	10
Intercompany payable	300	300
Credit derivative liabilities	403	458
Deferred tax liabilities, net	0	0
Financial guaranty variable interest entities’ liabilities, at fair value	855	958
Dividend payable to affiliate	0	0
Other	857	665
Total liabilities	8,715	8,475
Effect on shareholders' equity (decrease) increase	7,687	7,405
Noncontrolling interest	299	296
Total shareholders' equity	7,986	7,701
Total liabilities and shareholders’ equity	16,701	16,176
Consolidating Adjustments [Member]
Assets
Total investment portfolio and cash	(359)	(368)
Investment in subsidiaries	(16,460)	(15,890)
Premiums receivable, net of commissions payable	(132)	(123)
Ceded unearned premium reserve	(894)	(893)
Deferred acquisition costs	(49)	(50)
Reinsurance recoverable on unpaid losses	(309)	(404)
Credit derivative assets	(44)	(56)
Deferred tax asset, net	(102)	(116)
Intercompany receivable	(70)	(70)
Financial guaranty variable interest entities’ assets, at fair value	0	0
Dividend receivable from affiliate	(125)	(300)
Other	(247)	(222)
Total assets	(18,791)	(18,492)
Liabilities and shareholders’ equity
Unearned premium reserve	(973)	(977)
Loss and loss adjustment expense reserve	(298)	(469)
Long-term debt	0	0
Intercompany payable	(370)	(370)
Credit derivative liabilities	(44)	(56)
Deferred tax liabilities, net	(88)	(88)
Financial guaranty variable interest entities’ liabilities, at fair value	0	0
Dividend payable to affiliate	(125)	(300)
Other	(410)	(346)
Total liabilities	(2,308)	(2,606)
Effect on shareholders' equity (decrease) increase	(16,184)	(15,590)
Noncontrolling interest	(299)	(296)
Total shareholders' equity	(16,483)	(15,886)
Total liabilities and shareholders’ equity	$ (18,791)	$ (18,492)