Subsidiary Information (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Revenues
Net earned premiums	$ 218	$ 222	$ 219	$ 194	$ 225	$ 211	$ 230	$ 254	$ 853	[1]	$ 920	[1]	$ 1,187	[1]
Net investment income	103	102	101	98	101	95	103	97	404		396		361
Net realized investment gains (losses)	1	2	(3)	1	(5)	(11)	(5)	3	1		(18)		(2)
Net change in fair value of credit derivatives:
Realized gains (losses) and other settlements									(108)		6		153
Net unrealized gains (losses)									(477)		554		(155)
Net change in fair value of credit derivatives	(119)	(36)	261	(691)	(295)	1,156	(65)	(236)	(585)		560		(2)
Equity in earnings of subsidiaries									0		0		0
Other									300		(39)		(231)
Total revenues									973		1,819		1,313
Expenses
Loss and LAE	64	90	122	247	149	215	124	(26)	523		462		412
Amortization of DAC	0	4	5	5	4	4	6	3	14		17		22
Interest expense	21	21	25	25	25	25	24	25	92		99		100
Other operating expenses									212		212		245
Total expenses									841		790		779
Income (loss) before income taxes	95	179	554	(696)	(148)	1,055	(91)	213	132		1,029		534
Provision (benefit) for income taxes	21	37	177	(213)	(64)	294	(48)	74	22		256		50
Net income (loss) attributable to Assured Guaranty Ltd.									110		773		484
Comprehensive income (loss)									257		1,029		454
Financial Guaranty Insurance Contracts, Net Premiums Receivable Adjustment Accretion of Discount on Net Premium Receivable									36		32		43
Assured Guaranty Ltd. (Parent)
Revenues
Net investment income									0		0		0
Net realized investment gains (losses)									0		0		0
Net change in fair value of credit derivatives:
Equity in earnings of subsidiaries									131		798		508
Other									0		0
Total revenues									131		798		508
Expenses
Interest expense									0		0		0
Other operating expenses									21		25		24
Total expenses									21		25		24
Income (loss) before income taxes									110		773		484
Provision (benefit) for income taxes									0		0		0
Net income (loss) attributable to Assured Guaranty Ltd.									110		773		484
Comprehensive income (loss)									257		1,029		454
AGUS (Issuer)
Revenues
Net investment income									0		0		0
Net realized investment gains (losses)									0		0		0
Net change in fair value of credit derivatives:
Equity in earnings of subsidiaries									177		640		443
Other									0		0
Total revenues									177		640		443
Expenses
Interest expense									35		39		39
Other operating expenses									2		1		3
Total expenses									37		40		42
Income (loss) before income taxes									140		600		401
Provision (benefit) for income taxes									(13)		(14)		(15)
Net income (loss) attributable to Assured Guaranty Ltd.									153		614		416
Comprehensive income (loss)									266		824		341
AGMH (Issuer)
Revenues
Net investment income									1		1		0
Net realized investment gains (losses)									0		0		0
Net change in fair value of credit derivatives:
Equity in earnings of subsidiaries									424		398		525
Other									0		0
Total revenues									425		399		525
Expenses
Interest expense									54		54		54
Other operating expenses									1		1		3
Total expenses									55		55		57
Income (loss) before income taxes									370		344		468
Provision (benefit) for income taxes									(19)		(19)		(21)
Net income (loss) attributable to Assured Guaranty Ltd.									389		363		489
Comprehensive income (loss)									465		507		428
Other Subsidiaries
Revenues
Net earned premiums									833		904		1,168
Net investment income									422		410		384
Net realized investment gains (losses)									1		(18)		(6)
Net change in fair value of credit derivatives:
Realized gains (losses) and other settlements									(108)		6		153
Net unrealized gains (losses)									(477)		554		(155)
Net change in fair value of credit derivatives									(585)		560		(2)
Equity in earnings of subsidiaries									153		614		416
Other									303		(34)		(230)
Total revenues									1,127		2,436		1,730
Expenses
Loss and LAE									528		454		406
Amortization of DAC									28		37		30
Interest expense									22		21		28
Other operating expenses									194		194		217
Total expenses									772		706		681
Income (loss) before income taxes									355		1,730		1,049
Provision (benefit) for income taxes									38		277		74
Net income (loss) attributable to Assured Guaranty Ltd.									317		1,453		975
Comprehensive income (loss)									577		1,918		1,036
Consolidating Adjustments
Revenues
Net earned premiums									20		16		19
Net investment income									(19)		(15)		(23)
Net realized investment gains (losses)									0		0		4
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
Equity in earnings of subsidiaries									(885)		(2,450)		(1,892)
Other									(3)		(5)		(1)
Total revenues									(887)		(2,454)		(1,893)
Expenses
Loss and LAE									(5)		8		6
Amortization of DAC									(14)		(20)		(8)
Interest expense									(19)		(15)		(21)
Other operating expenses									(6)		(9)		(2)
Total expenses									(44)		(36)		(25)
Income (loss) before income taxes									(843)		(2,418)		(1,868)
Provision (benefit) for income taxes									16		12		12
Net income (loss) attributable to Assured Guaranty Ltd.									(859)		(2,430)		(1,880)
Comprehensive income (loss)									(1,308)		(3,249)		(1,805)
Financial guaranty
Condensed financial statements
Scheduled net earned premiums									581		765		1,054
Expenses
Acceleration of premium earnings									249		125		90
Financial Guaranty Insurance Contracts, Net Premiums Receivable Adjustment Accretion of Discount on Net Premium Receivable									(22)		(28)		(40)
Total financial guaranty insurance									852		918		1,184
Other
Revenues
Net earned premiums									$ 1		$ 2		$ 3

[1] Excludes $153 million, $75 million and $48 million for the year ended December 31, 2012, 2011 and 2010, respectively, related to consolidated FG VIEs.