Subsidiary Information (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012
Revenues
Net earned premiums	$ 248	[1]	$ 194	[1]
Net investment income	94		98
Net realized investment gains (losses)	28		1
Net change in fair value of credit derivatives:
Realized gains (losses) and other settlements	18		(57)
Net unrealized gains (losses)	(610)		(634)
Net change in fair value of credit derivatives	(592)		(691)
Equity in earnings of subsidiaries	0		0
Other	46		36
Total revenues	(176)		(362)
Expenses
Loss and LAE	(48)		242
Amortization of DAC	3		5
Interest expense	21		25
Other operating expenses	60		62
Total expenses	36		334
Income (loss) before income taxes	(212)		(696)
Provision (benefit) for income taxes	(68)		(213)
Net income (loss) attributable to Assured Guaranty Ltd.	(144)		(483)
Comprehensive income (loss)	(212)		(452)
Financial Guaranty Insurance Contracts, Net Premiums Receivable Adjustment Accretion of Discount on Net Premium Receivable	9		6
Assured Guaranty Ltd. (Parent)
Revenues
Net investment income	0		0
Net realized investment gains (losses)	0		0
Net change in fair value of credit derivatives:
Equity in earnings of subsidiaries	(139)		(476)
Other	0		0
Total revenues	(139)		(476)
Expenses
Interest expense	0		0
Other operating expenses	5		7
Total expenses	5		7
Income (loss) before income taxes	(144)		(483)
Provision (benefit) for income taxes	0		0
Net income (loss) attributable to Assured Guaranty Ltd.	(144)		(483)
Comprehensive income (loss)	(212)		(452)
AGUS (Issuer)
Revenues
Net investment income	0		0
Net realized investment gains (losses)	0		0
Net change in fair value of credit derivatives:
Equity in earnings of subsidiaries	(82)		(353)
Other	0		0
Total revenues	(82)		(353)
Expenses
Interest expense	7		10
Other operating expenses	0		1
Total expenses	7		11
Income (loss) before income taxes	(89)		(364)
Provision (benefit) for income taxes	(3)		(4)
Net income (loss) attributable to Assured Guaranty Ltd.	(86)		(360)
Comprehensive income (loss)	(137)		(335)
AGMH (Issuer)
Revenues
Net investment income	0		0
Net realized investment gains (losses)	0		0
Net change in fair value of credit derivatives:
Equity in earnings of subsidiaries	162		(7)
Other	0		0
Total revenues	162		(7)
Expenses
Interest expense	13		13
Other operating expenses	0		0
Total expenses	13		13
Income (loss) before income taxes	149		(20)
Provision (benefit) for income taxes	(5)		(12)
Net income (loss) attributable to Assured Guaranty Ltd.	154		(8)
Comprehensive income (loss)	117		9
Other Subsidiaries
Revenues
Net earned premiums	246		189
Net investment income	99		101
Net realized investment gains (losses)	28		1
Net change in fair value of credit derivatives:
Realized gains (losses) and other settlements	18		(57)
Net unrealized gains (losses)	(610)		(634)
Net change in fair value of credit derivatives	(592)		(691)
Equity in earnings of subsidiaries	0		(360)
Other	47		36
Total revenues	(172)		(724)
Expenses
Loss and LAE	(44)		244
Amortization of DAC	8		9
Interest expense	6		5
Other operating expenses	58		55
Total expenses	28		313
Income (loss) before income taxes	(200)		(1,037)
Provision (benefit) for income taxes	(65)		(208)
Net income (loss) attributable to Assured Guaranty Ltd.	(135)		(829)
Comprehensive income (loss)	(253)		(773)
Consolidating Adjustments
Revenues
Net earned premiums	2		5
Net investment income	(5)		(3)
Net realized investment gains (losses)	0		0
Net change in fair value of credit derivatives:
Realized gains (losses) and other settlements	0		0
Net unrealized gains (losses)	0		0
Net change in fair value of credit derivatives	0		0
Equity in earnings of subsidiaries	59		1,196
Other	(1)		0
Total revenues	55		1,198
Expenses
Loss and LAE	(4)		(2)
Amortization of DAC	(5)		(4)
Interest expense	(5)		(3)
Other operating expenses	(3)		(1)
Total expenses	(17)		(10)
Income (loss) before income taxes	72		1,208
Provision (benefit) for income taxes	5		11
Net income (loss) attributable to Assured Guaranty Ltd.	67		1,197
Comprehensive income (loss)	273		1,099
Financial guaranty
Condensed financial statements
Scheduled net earned premiums	128		152
Expenses
Acceleration of premium earnings	113		37
Financial Guaranty Insurance Contracts, Net Premiums Receivable Adjustment Accretion of Discount on Net Premium Receivable	(7)		(5)
Total financial guaranty insurance	248		194
Other
Revenues
Net earned premiums	$ 0		$ 0

[1] Excludes $18 million and $17 million for First Quarter 2013 and 2012, respectively, related to consolidated FG VIEs.