Subsidiary Information - Condensed Consolidating Balance Sheet (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Assets
Total investment portfolio and cash	$ 11,199	$ 11,459
Investment in subsidiaries	0	0
Premiums receivable, net of commissions payable	700	729
Ceded unearned premium reserve	365	381
Deferred acquisition costs	120	121
Reinsurance recoverable on unpaid losses	77	78
Credit derivative assets	77	68
Deferred tax asset, net	218	260
Intercompany receivable	0	0
Financial guaranty variable interest entities’ assets, at fair value	1,499	1,402
Other	422	427
Total assets	14,677	14,925
Liabilities and shareholders’ equity
Unearned premium reserve	4,127	4,261
Loss and loss adjustment expense reserve	787	799
Long-term debt	1,304	1,303
Intercompany payable	0	0
Credit derivative liabilities	859	963
Deferred tax liabilities, net	0	0
Financial guaranty variable interest entities’ liabilities, at fair value	1,423	1,419
Other	391	422
Total liabilities	8,891	9,167
Effect on shareholders’ equity (decrease) increase	5,786	5,758
Noncontrolling interest	0	0
Total shareholders' equity	5,786	5,758
Total liabilities and shareholders’ equity	14,677	14,925
Reportable Legal Entities [Member] | Assured Guaranty Ltd. (Parent) [Member]
Assets
Total investment portfolio and cash	47	126
Investment in subsidiaries	5,722	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	21	27
Total assets	5,790	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	4	7
Total liabilities	4	7
Effect on shareholders’ equity (decrease) increase	5,786	5,758
Noncontrolling interest	0	0
Total shareholders' equity	5,786	5,758
Total liabilities and shareholders’ equity	5,790	5,765
Reportable Legal Entities [Member] | AGUS (Issuer) [Member]
Assets
Total investment portfolio and cash	82	204
Investment in subsidiaries	5,087	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	56	54
Intercompany receivable	200	0
Financial guaranty variable interest entities’ assets, at fair value	0	0
Other	79	77
Total assets	5,504	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	23	9
Total liabilities	960	946
Effect on shareholders’ equity (decrease) increase	4,544	4,461
Noncontrolling interest	0	0
Total shareholders' equity	4,544	4,461
Total liabilities and shareholders’ equity	5,504	5,407
Reportable Legal Entities [Member] | AGMH (Issuer) [Member]
Assets
Total investment portfolio and cash	23	47
Investment in subsidiaries	3,955	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	31	27
Total assets	4,009	4,039
Liabilities and shareholders’ equity
Unearned premium reserve	0	0
Loss and loss adjustment expense reserve	0	0
Long-term debt	439	437
Intercompany payable	0	0
Credit derivative liabilities	0	0
Deferred tax liabilities, net	93	94
Financial guaranty variable interest entities’ liabilities, at fair value	0	0
Other	22	16
Total liabilities	554	547
Effect on shareholders’ equity (decrease) increase	3,455	3,492
Noncontrolling interest	0	0
Total shareholders' equity	3,455	3,492
Total liabilities and shareholders’ equity	4,009	4,039
Reportable Legal Entities [Member] | Other Entities [Member]
Assets
Total investment portfolio and cash	11,347	11,382
Investment in subsidiaries	350	339
Premiums receivable, net of commissions payable	830	864
Ceded unearned premium reserve	1,430	1,469
Deferred acquisition costs	184	186
Reinsurance recoverable on unpaid losses	344	338
Credit derivative assets	262	277
Deferred tax asset, net	251	295
Intercompany receivable	90	90
Financial guaranty variable interest entities’ assets, at fair value	1,499	1,402
Other	522	538
Total assets	17,109	17,180
Liabilities and shareholders’ equity
Unearned premium reserve	5,173	5,328
Loss and loss adjustment expense reserve	1,062	1,066
Long-term debt	18	19
Intercompany payable	500	300
Credit derivative liabilities	1,044	1,172
Deferred tax liabilities, net	0	0
Financial guaranty variable interest entities’ liabilities, at fair value	1,423	1,419
Other	702	764
Total liabilities	9,922	10,068
Effect on shareholders’ equity (decrease) increase	6,837	6,773
Noncontrolling interest	350	339
Total shareholders' equity	7,187	7,112
Total liabilities and shareholders’ equity	17,109	17,180
Consolidating Adjustments [Member]
Assets
Total investment portfolio and cash	(300)	(300)
Investment in subsidiaries	(15,114)	(14,988)
Premiums receivable, net of commissions payable	(130)	(135)
Ceded unearned premium reserve	(1,065)	(1,088)
Deferred acquisition costs	(64)	(65)
Reinsurance recoverable on unpaid losses	(267)	(260)
Credit derivative assets	(185)	(209)
Deferred tax asset, net	(89)	(89)
Intercompany receivable	(290)	(90)
Financial guaranty variable interest entities’ assets, at fair value	0	0
Other	(231)	(242)
Total assets	(17,735)	(17,466)
Liabilities and shareholders’ equity
Unearned premium reserve	(1,046)	(1,067)
Loss and loss adjustment expense reserve	(275)	(267)
Long-term debt	0	0
Intercompany payable	(590)	(390)
Credit derivative liabilities	(185)	(209)
Deferred tax liabilities, net	(93)	(94)
Financial guaranty variable interest entities’ liabilities, at fair value	0	0
Other	(360)	(374)
Total liabilities	(2,549)	(2,401)
Effect on shareholders’ equity (decrease) increase	(14,836)	(14,726)
Noncontrolling interest	(350)	(339)
Total shareholders' equity	(15,186)	(15,065)
Total liabilities and shareholders’ equity	$ (17,735)	$ (17,466)