Subsidiary Information - Condensed Consolidating Balance Sheet (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Assets
Total investment portfolio and cash	$ 11,471	$ 11,103
Investment in subsidiaries	0	0
Premiums receivable, net of commissions payable	916	576
Ceded unearned premium reserve	174	206
Deferred acquisition costs	107	106
Reinsurance recoverable on unpaid losses	78	80
Credit derivative assets	6	13
Deferred tax asset, net	391	497
Intercompany receivable	0	0
Financial guaranty variable interest entities’ assets, at fair value	757	876
Dividend receivable from affiliate	0	0
Other	755	694
Total assets	14,655	14,151
Liabilities and shareholders’ equity
Unearned premium reserve	3,748	3,511
Loss and loss adjustment expense reserve	1,268	1,127
Long-term debt	1,294	1,306
Intercompany payable	0	0
Credit derivative liabilities	367	402
Deferred tax liabilities, net	0	0
Financial guaranty variable interest entities’ liabilities, at fair value	820	958
Dividend payable to affiliate	0	0
Other	408	343
Total liabilities	7,905	7,647
Effect on shareholders' equity (decrease) increase	6,750	6,504
Noncontrolling interest	0	0
Total shareholders' equity	6,750	6,504
Total liabilities and shareholders’ equity	14,655	14,151
AGUS [Member]
Liabilities and shareholders’ equity
Long-term debt	843	843
AGMH [Member]
Liabilities and shareholders’ equity
Long-term debt	456	453
Reportable Legal Entities [Member] | Assured Guaranty Ltd. (Parent) [Member]
Assets
Total investment portfolio and cash	27	36
Investment in subsidiaries	6,713	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	0	300
Other	16	11
Total assets	6,756	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	6	7
Total liabilities	6	7
Effect on shareholders' equity (decrease) increase	6,750	6,504
Noncontrolling interest	0	0
Total shareholders' equity	6,750	6,504
Total liabilities and shareholders’ equity	6,756	6,511
Reportable Legal Entities [Member] | Issuer Subsidiary [Member] | AGUS [Member]
Assets
Total investment portfolio and cash	144	384
Investment in subsidiaries	6,083	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	119	78
Total assets	6,346	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	3	0
Financial guaranty variable interest entities’ liabilities, at fair value	0	0
Dividend payable to affiliate	0	300
Other	24	3
Total liabilities	940	1,216
Effect on shareholders' equity (decrease) increase	5,406	4,958
Noncontrolling interest	0	0
Total shareholders' equity	5,406	4,958
Total liabilities and shareholders’ equity	6,346	6,174
Reportable Legal Entities [Member] | Issuer Subsidiary [Member] | AGMH [Member]
Assets
Total investment portfolio and cash	28	22
Investment in subsidiaries	4,096	3,799
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	45	26
Total assets	4,169	3,847
Liabilities and shareholders’ equity
Unearned premium reserve	0	0
Loss and loss adjustment expense reserve	0	0
Long-term debt	456	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	22	14
Total liabilities	565	555
Effect on shareholders' equity (decrease) increase	3,604	3,292
Noncontrolling interest	0	0
Total shareholders' equity	3,604	3,292
Total liabilities and shareholders’ equity	4,169	3,847
Reportable Legal Entities [Member] | Other Entities [Member]
Assets
Total investment portfolio and cash	11,593	11,029
Investment in subsidiaries	302	296
Premiums receivable, net of commissions payable	1,049	699
Ceded unearned premium reserve	1,058	1,099
Deferred acquisition costs	153	156
Reinsurance recoverable on unpaid losses	394	484
Credit derivative assets	51	69
Deferred tax asset, net	491	597
Intercompany receivable	70	70
Financial guaranty variable interest entities’ assets, at fair value	757	876
Dividend receivable from affiliate	0	0
Other	907	801
Total assets	16,825	16,176
Liabilities and shareholders’ equity
Unearned premium reserve	4,707	4,488
Loss and loss adjustment expense reserve	1,548	1,596
Long-term debt	9	10
Intercompany payable	300	300
Credit derivative liabilities	412	458
Deferred tax liabilities, net	0	0
Financial guaranty variable interest entities’ liabilities, at fair value	820	958
Dividend payable to affiliate	0	0
Other	821	665
Total liabilities	8,617	8,475
Effect on shareholders' equity (decrease) increase	7,906	7,405
Noncontrolling interest	302	296
Total shareholders' equity	8,208	7,701
Total liabilities and shareholders’ equity	16,825	16,176
Consolidation, Eliminations [Member]
Assets
Total investment portfolio and cash	(321)	(368)
Investment in subsidiaries	(17,194)	(15,955)
Premiums receivable, net of commissions payable	(133)	(123)
Ceded unearned premium reserve	(884)	(893)
Deferred acquisition costs	(46)	(50)
Reinsurance recoverable on unpaid losses	(316)	(404)
Credit derivative assets	(45)	(56)
Deferred tax asset, net	(100)	(116)
Intercompany receivable	(70)	(70)
Financial guaranty variable interest entities’ assets, at fair value	0	0
Dividend receivable from affiliate	0	(300)
Other	(332)	(222)
Total assets	(19,441)	(18,557)
Liabilities and shareholders’ equity
Unearned premium reserve	(959)	(977)
Loss and loss adjustment expense reserve	(280)	(469)
Long-term debt	(14)	0
Intercompany payable	(370)	(370)
Credit derivative liabilities	(45)	(56)
Deferred tax liabilities, net	(90)	(88)
Financial guaranty variable interest entities’ liabilities, at fair value	0	0
Dividend payable to affiliate	0	(300)
Other	(465)	(346)
Total liabilities	(2,223)	(2,606)
Effect on shareholders' equity (decrease) increase	(16,916)	(15,655)
Noncontrolling interest	(302)	(296)
Total shareholders' equity	(17,218)	(15,951)
Total liabilities and shareholders’ equity	$ (19,441)	$ (18,557)