Subsidiary Information - Condensed Consolidating Balance Sheet (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Assets
Total investment portfolio and cash	$ 11,663	$ 11,103
Investment in subsidiaries	0	0
Premiums receivable, net of commissions payable	922	576
Ceded unearned premium reserve	108	206
Deferred acquisition costs	105	106
Reinsurance recoverable on unpaid losses	39	80
Credit derivative assets	3	13
Deferred tax asset, net	135	497
Intercompany receivable	0	0
Financial guaranty variable interest entities’ assets, at fair value	707	876
Dividend receivable from affiliate	0	0
Other	967	694
Total assets	14,649	14,151
Liabilities and shareholders’ equity
Unearned premium reserve	3,597	3,511
Loss and loss adjustment expense reserve	1,326	1,127
Long-term debt	1,292	1,306
Intercompany payable	0	0
Credit derivative liabilities	305	402
Deferred tax liabilities, net	0	0
Financial guaranty variable interest entities’ liabilities, at fair value	768	958
Dividend payable to affiliate	0	0
Other	483	343
Total liabilities	7,771	7,647
Effect on shareholders' equity (decrease) increase	6,878	6,504
Noncontrolling interest	0	0
Total shareholders' equity	6,878	6,504
Total liabilities and shareholders’ equity	14,649	14,151
AGUS [Member]
Liabilities and shareholders’ equity
Long-term debt	843	843
AGMH [Member]
Liabilities and shareholders’ equity
Long-term debt	459	453
Reportable Legal Entities [Member] | Assured Guaranty Ltd. (Parent) [Member]
Assets
Total investment portfolio and cash	47	36
Investment in subsidiaries	6,799	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	25	300
Other	22	11
Total assets	6,893	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	15	7
Total liabilities	15	7
Effect on shareholders' equity (decrease) increase	6,878	6,504
Noncontrolling interest	0	0
Total shareholders' equity	6,878	6,504
Total liabilities and shareholders’ equity	6,893	6,511
Reportable Legal Entities [Member] | Issuer Subsidiary [Member] | AGUS [Member]
Assets
Total investment portfolio and cash	143	384
Investment in subsidiaries	6,257	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	76	16
Intercompany receivable	0	0
Financial guaranty variable interest entities’ assets, at fair value	0	0
Dividend receivable from affiliate	0	0
Other	28	78
Total assets	6,504	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	0	0
Financial guaranty variable interest entities’ liabilities, at fair value	0	0
Dividend payable to affiliate	25	300
Other	19	3
Total liabilities	957	1,216
Effect on shareholders' equity (decrease) increase	5,547	4,958
Noncontrolling interest	0	0
Total shareholders' equity	5,547	4,958
Total liabilities and shareholders’ equity	6,504	6,174
Reportable Legal Entities [Member] | Issuer Subsidiary [Member] | AGMH [Member]
Assets
Total investment portfolio and cash	24	22
Investment in subsidiaries	4,216	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	51	26
Total assets	4,291	3,847
Liabilities and shareholders’ equity
Unearned premium reserve	0	0
Loss and loss adjustment expense reserve	0	0
Long-term debt	459	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	568	555
Effect on shareholders' equity (decrease) increase	3,723	3,292
Noncontrolling interest	0	0
Total shareholders' equity	3,723	3,292
Total liabilities and shareholders’ equity	4,291	3,847
Reportable Legal Entities [Member] | Other Entities [Member]
Assets
Total investment portfolio and cash	11,776	11,029
Investment in subsidiaries	208	296
Premiums receivable, net of commissions payable	1,076	699
Ceded unearned premium reserve	1,009	1,099
Deferred acquisition costs	150	156
Reinsurance recoverable on unpaid losses	394	484
Credit derivative assets	50	69
Deferred tax asset, net	153	597
Intercompany receivable	70	70
Financial guaranty variable interest entities’ assets, at fair value	707	876
Dividend receivable from affiliate	0	0
Other	1,100	801
Total assets	16,693	16,176
Liabilities and shareholders’ equity
Unearned premium reserve	4,565	4,488
Loss and loss adjustment expense reserve	1,646	1,596
Long-term debt	8	10
Intercompany payable	300	300
Credit derivative liabilities	352	458
Deferred tax liabilities, net	0	0
Financial guaranty variable interest entities’ liabilities, at fair value	768	958
Dividend payable to affiliate	0	0
Other	815	665
Total liabilities	8,454	8,475
Effect on shareholders' equity (decrease) increase	8,031	7,405
Noncontrolling interest	208	296
Total shareholders' equity	8,239	7,701
Total liabilities and shareholders’ equity	16,693	16,176
Consolidation, Eliminations [Member]
Assets
Total investment portfolio and cash	(327)	(368)
Investment in subsidiaries	(17,480)	(15,955)
Premiums receivable, net of commissions payable	(154)	(123)
Ceded unearned premium reserve	(901)	(893)
Deferred acquisition costs	(45)	(50)
Reinsurance recoverable on unpaid losses	(355)	(404)
Credit derivative assets	(47)	(56)
Deferred tax asset, net	(94)	(116)
Intercompany receivable	(70)	(70)
Financial guaranty variable interest entities’ assets, at fair value	0	0
Dividend receivable from affiliate	(25)	(300)
Other	(234)	(222)
Total assets	(19,732)	(18,557)
Liabilities and shareholders’ equity
Unearned premium reserve	(968)	(977)
Loss and loss adjustment expense reserve	(320)	(469)
Long-term debt	(18)	0
Intercompany payable	(370)	(370)
Credit derivative liabilities	(47)	(56)
Deferred tax liabilities, net	(87)	(88)
Financial guaranty variable interest entities’ liabilities, at fair value	0	0
Dividend payable to affiliate	(25)	(300)
Other	(388)	(346)
Total liabilities	(2,223)	(2,606)
Effect on shareholders' equity (decrease) increase	(17,301)	(15,655)
Noncontrolling interest	(208)	(296)
Total shareholders' equity	(17,509)	(15,951)
Total liabilities and shareholders’ equity	$ (19,732)	$ (18,557)