Subsidiary Information - Condensed Consolidating Balance Sheet (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014		Dec. 31, 2013	Sep. 30, 2013		Dec. 31, 2012
Assets
Total investment portfolio and cash	$ 11,531		$ 10,969
Investment in subsidiaries	0		0
Premiums receivable, net of commissions payable	801	[1]	876	906	[1]	1,005
Ceded unearned premium reserve	420		452
Deferred acquisition costs	120		124
Reinsurance recoverable on unpaid losses	56		36
Credit derivative assets	86		94
Deferred tax asset, net	474		688
Intercompany receivable	0		0
Financial guaranty variable interest entities’ assets, at fair value	1,296		2,565
Other	585		483
Total assets	15,369		16,287
Liabilities and shareholders’ equity
Unearned premium reserve	4,263		4,595
Loss and loss adjustment expense reserve	760		592
Long-term debt	1,303		816
Intercompany payable	0		0
Credit derivative liabilities	1,654		1,787
Deferred tax liabilities, net	0		0
Financial guaranty variable interest entities’ liabilities, at fair value	1,459		2,871
Other	576		511
Total liabilities	10,015		11,172
TOTAL SHAREHOLDERS’ EQUITY ATTRIBUTABLE TO ASSURED GUARANTY LTD.	5,354		5,115
Noncontrolling interest	0		0
TOTAL SHAREHOLDERS' EQUITY	5,354		5,115
Total liabilities and shareholders’ equity	15,369		16,287
Assured Guaranty Ltd. (Parent)
Assets
Total investment portfolio and cash	298		33
Investment in subsidiaries	5,035		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	5,360		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	6		7
Total liabilities	6		7
TOTAL SHAREHOLDERS’ EQUITY ATTRIBUTABLE TO ASSURED GUARANTY LTD.	5,354		5,115
Noncontrolling interest	0		0
TOTAL SHAREHOLDERS' EQUITY	5,354		5,115
Total liabilities and shareholders’ equity	5,360		5,122
AGUS (Issuer)
Assets
Total investment portfolio and cash	150		186
Investment in subsidiaries	4,677		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	98		97
Intercompany receivable	0		0
Financial guaranty variable interest entities’ assets, at fair value	0		0
Other	29		17
Total assets	4,954		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	22		7
Total liabilities	959		445
TOTAL SHAREHOLDERS’ EQUITY ATTRIBUTABLE TO ASSURED GUARANTY LTD.	3,995		4,046
Noncontrolling interest	0		0
TOTAL SHAREHOLDERS' EQUITY	3,995		4,046
Total liabilities and shareholders’ equity	4,954		4,491
AGMH (Issuer)
Assets
Total investment portfolio and cash	28		42
Investment in subsidiaries	3,929		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	43		31
Total assets	4,000		3,647
Liabilities and shareholders’ equity
Unearned premium reserve	0		0
Loss and loss adjustment expense reserve	0		0
Long-term debt	436		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	21		16
Total liabilities	551		541
TOTAL SHAREHOLDERS’ EQUITY ATTRIBUTABLE TO ASSURED GUARANTY LTD.	3,449		3,106
Noncontrolling interest	0		0
TOTAL SHAREHOLDERS' EQUITY	3,449		3,106
Total liabilities and shareholders’ equity	4,000		3,647
Other Subsidiaries
Assets
Total investment portfolio and cash	11,355		11,008
Investment in subsidiaries	330		289
Premiums receivable, net of commissions payable	936		1,025
Ceded unearned premium reserve	1,513		1,598
Deferred acquisition costs	189		198
Reinsurance recoverable on unpaid losses	228		170
Credit derivative assets	436		482
Deferred tax asset, net	464		681
Intercompany receivable	90		90
Financial guaranty variable interest entities’ assets, at fair value	1,296		2,565
Other	709		638
Total assets	17,546		18,744
Liabilities and shareholders’ equity
Unearned premium reserve	5,336		5,720
Loss and loss adjustment expense reserve	938		733
Long-term debt	20		38
Intercompany payable	300		300
Credit derivative liabilities	2,004		2,175
Deferred tax liabilities, net	0		0
Financial guaranty variable interest entities’ liabilities, at fair value	1,459		2,871
Other	879		853
Total liabilities	10,936		12,690
TOTAL SHAREHOLDERS’ EQUITY ATTRIBUTABLE TO ASSURED GUARANTY LTD.	6,280		5,765
Noncontrolling interest	330		289
TOTAL SHAREHOLDERS' EQUITY	6,610		6,054
Total liabilities and shareholders’ equity	17,546		18,744
Consolidating Adjustments
Assets
Total investment portfolio and cash	(300)		(300)
Investment in subsidiaries	(13,971)		(13,120)
Premiums receivable, net of commissions payable	(135)		(149)
Ceded unearned premium reserve	(1,093)		(1,146)
Deferred acquisition costs	(69)		(74)
Reinsurance recoverable on unpaid losses	(172)		(134)
Credit derivative assets	(350)		(388)
Deferred tax asset, net	(88)		(90)
Intercompany receivable	(90)		(90)
Financial guaranty variable interest entities’ assets, at fair value	0		0
Other	(223)		(226)
Total assets	(16,491)		(15,717)
Liabilities and shareholders’ equity
Unearned premium reserve	(1,073)		(1,125)
Loss and loss adjustment expense reserve	(178)		(141)
Long-term debt	0		0
Intercompany payable	(390)		(390)
Credit derivative liabilities	(350)		(388)
Deferred tax liabilities, net	(94)		(95)
Financial guaranty variable interest entities’ liabilities, at fair value	0		0
Other	(352)		(372)
Total liabilities	(2,437)		(2,511)
TOTAL SHAREHOLDERS’ EQUITY ATTRIBUTABLE TO ASSURED GUARANTY LTD.	(13,724)		(12,917)
Noncontrolling interest	(330)		(289)
TOTAL SHAREHOLDERS' EQUITY	(14,054)		(13,206)
Total liabilities and shareholders’ equity	$ (16,491)		$ (15,717)

[1] Excludes $18 million and $19 million as of September 30, 2014 and September 30, 2013, respectively, related to consolidated FG VIEs.