Subsidiary Information - Condensed Consolidating Statement of Operations (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Revenues
Net earned premiums	$ 158	$ 144	$ 136	$ 132	$ 182	$ 159	$ 163	$ 248	$ 570		$ 752		$ 853
Net investment income	102	102	96	103	107	99	93	94	403		393		404
Net realized investment gains (losses)	(35)	(19)	(8)	2	29	(7)	2	28	(60)		52		1
Net change in fair value of credit derivatives:
Realized gains (losses) and other settlements									23		(42)		(108)
Net unrealized gains (losses)									800	[1]	107	[1]	(477)	[1]
Net change in fair value of credit derivatives	676	255	103	(211)	229	354	74	(592)	823		65		(585)
Other									258		346		281
Total revenues									1,994		1,608		954
Expenses
Loss and LAE	72	(44)	57	41	85	55	62	(48)	126		154		504
Amortization of DAC	13	4	3	5	4	4	1	3	25		12		14
Interest expense	25	27	20	20	19	21	21	21	92		82		92
Other operating expenses	55	50	55	60	52	54	52	60	220		218		212
Total expenses									463		466		822
Income (loss) before income taxes	756	488	218	69	489	536	329	(212)	1,531		1,142		132
Total (provision) benefit for income taxes	(224)	(133)	(59)	(27)	(140)	(152)	(110)	68	(443)		(334)		(22)
Equity in net earnings of subsidiaries									0		0		0
Net income (loss)									1,088		808		110
Less: noncontrolling interest									0		0
Net income (loss)	532	355	159	42	349	384	219	(144)	1,088		808		110
Comprehensive income (loss)									1,298		453		257
Reportable Legal Entities [Member] | Assured Guaranty Ltd. (Parent) [Member]
Revenues
Net earned premiums									0		0		0
Net investment income									0		0		0
Net realized investment gains (losses)									0		0		0
Net change in fair value of credit derivatives:
Realized gains (losses) and other settlements									0		0		0
Net unrealized gains (losses)									0		0		0
Net change in fair value of credit derivatives									0		0		0
Other									0		0		0
Total revenues									0		0		0
Expenses
Loss and LAE									0		0		0
Amortization of DAC									0		0		0
Interest expense									0		0		0
Other operating expenses									31		22		21
Total expenses									31		22		21
Income (loss) before income taxes									(31)		(22)		(21)
Total (provision) benefit for income taxes									0		0		0
Equity in net earnings of subsidiaries									1,119		830		131
Net income (loss)									1,088		808		110
Less: noncontrolling interest									0		0
Net income (loss)									1,088		808
Comprehensive income (loss)									1,298		453		257
Reportable Legal Entities [Member] | AGUS (Issuer) [Member]
Revenues
Net earned premiums									0		0		0
Net investment income									0		0		0
Net realized investment gains (losses)									0		0		0
Net change in fair value of credit derivatives:
Realized gains (losses) and other settlements									0		0		0
Net unrealized gains (losses)									0		0		0
Net change in fair value of credit derivatives									0		0		0
Other									0		0		0
Total revenues									0		0		0
Expenses
Loss and LAE									0		0		0
Amortization of DAC									0		0		0
Interest expense									40		28		35
Other operating expenses									1		1		2
Total expenses									41		29		37
Income (loss) before income taxes									(41)		(29)		(37)
Total (provision) benefit for income taxes									14		9		13
Equity in net earnings of subsidiaries									983		768		177
Net income (loss)									956		748		153
Less: noncontrolling interest									0		0
Net income (loss)									956		748
Comprehensive income (loss)									1,114		522		266
Reportable Legal Entities [Member] | AGMH (Issuer) [Member]
Revenues
Net earned premiums									0		0		0
Net investment income									1		1		1
Net realized investment gains (losses)									0		0		0
Net change in fair value of credit derivatives:
Realized gains (losses) and other settlements									0		0		0
Net unrealized gains (losses)									0		0		0
Net change in fair value of credit derivatives									0		0		0
Other									0		0		0
Total revenues									1		1		1
Expenses
Loss and LAE									0		0		0
Amortization of DAC									0		0		0
Interest expense									54		54		54
Other operating expenses									1		1		1
Total expenses									55		55		55
Income (loss) before income taxes									(54)		(54)		(54)
Total (provision) benefit for income taxes									19		17		19
Equity in net earnings of subsidiaries									513		701		424
Net income (loss)									478		664		389
Less: noncontrolling interest									0		0
Net income (loss)									478		664
Comprehensive income (loss)									577		515		465
Reportable Legal Entities [Member] | Other Entities [Member]
Revenues
Net earned premiums									566		740		833
Net investment income									412		408		422
Net realized investment gains (losses)									(58)		87		1
Net change in fair value of credit derivatives:
Realized gains (losses) and other settlements									23		(42)		(108)
Net unrealized gains (losses)									800		107		(477)
Net change in fair value of credit derivatives									823		65		(585)
Other									259		348		284
Total revenues									2,002		1,648		955
Expenses
Loss and LAE									122		144		509
Amortization of DAC									33		12		28
Interest expense									16		20		22
Other operating expenses									195		199		194
Total expenses									366		375		753
Income (loss) before income taxes									1,636		1,273		202
Total (provision) benefit for income taxes									(469)		(387)		(38)
Equity in net earnings of subsidiaries									32		19		153
Net income (loss)									1,199		905		317
Less: noncontrolling interest									32		19
Net income (loss)									1,167		886
Comprehensive income (loss)									1,570		309		577
Consolidating Adjustments [Member]
Revenues
Net earned premiums									4		12		20
Net investment income									(10)		(16)		(19)
Net realized investment gains (losses)									(2)		(35)		0
Net change in fair value of credit derivatives:
Realized gains (losses) and other settlements									0		0		0
Net unrealized gains (losses)									0		0		0
Net change in fair value of credit derivatives									0		0		0
Other									(1)		(2)		(3)
Total revenues									(9)		(41)		(2)
Expenses
Loss and LAE									4		10		(5)
Amortization of DAC									(8)		0		(14)
Interest expense									(18)		(20)		(19)
Other operating expenses									(8)		(5)		(6)
Total expenses									(30)		(15)		(44)
Income (loss) before income taxes									21		(26)		42
Total (provision) benefit for income taxes									(7)		27		(16)
Equity in net earnings of subsidiaries									(2,647)		(2,318)		(885)
Net income (loss)									(2,633)		(2,317)		(859)
Less: noncontrolling interest									(32)		(19)
Net income (loss)									(2,601)		(2,298)
Comprehensive income (loss)									$ (3,261)		$ (1,346)		$ (1,308)

[1] Except for net estimated credit impairments (i.e., net expected loss to be paid as discussed in Note 6), the unrealized gains and losses on credit derivatives are expected to reduce to zero as the exposure approaches its maturity date. With considerable volatility continuing in the market, unrealized gains (losses) on credit derivatives may fluctuate significantly in future periods.