Subsidiary Information (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013		Dec. 31, 2012	Mar. 31, 2012		Dec. 31, 2011
Assets
Total investment portfolio and cash	$ 10,987		$ 11,223
Investment in subsidiaries	0		0
Premiums Receivable, at Carrying Value	956	[1]	1,005	1,019	[1]	1,003
Ceded unearned premium reserve	535		561
Deferred acquisition costs	116		116
Reinsurance recoverable on unpaid losses	56		58
Credit Risk Derivative Assets, at Fair Value	125		141
Net deferred income tax asset	872		721
Intercompany receivable	0		0
Financial guaranty variable interest entities’ assets, at fair value	2,813		2,688
Other	839		729
Total assets	17,299		17,242
Liabilities and shareholders’ equity
Unearned premium reserves	4,982		5,207
Loss and loss adjustment expense reserve	532		601
Long-term debt	832		836
Intercompany payable	0		0
Credit derivative liabilities	2,518		1,934
Financial guaranty variable interest entities' liabilities, at fair value	3,178		3,141
Other	533		529
Total liabilities	12,575		12,248
Total shareholders' equity	4,724		4,994
Total liabilities and shareholders' equity	17,299		17,242
Assured Guaranty Ltd. (Parent)
Assets
Total investment portfolio and cash	212		245
Investment in subsidiaries	4,487		4,734
Net deferred income tax asset	0		0
Intercompany receivable	0		0
Other	31		23
Total assets	4,730		5,002
Liabilities and shareholders’ equity
Long-term debt	0		0
Intercompany payable	0		0
Other	6		8
Total liabilities	6		8
Total shareholders' equity	4,724		4,994
Total liabilities and shareholders' equity	4,730		5,002
AGUS (Issuer)
Assets
Total investment portfolio and cash	15		15
Investment in subsidiaries	3,826		3,958
Net deferred income tax asset	48		48
Intercompany receivable	0		0
Other	2		29
Total assets	3,891		4,050
Liabilities and shareholders’ equity
Long-term debt	348		347
Intercompany payable	173		173
Credit derivative liabilities	0		0
Other	(16)		6
Total liabilities	505		526
Total shareholders' equity	3,386		3,524
Total liabilities and shareholders' equity	3,891		4,050
AGMH (Issuer)
Assets
Total investment portfolio and cash	48		30
Investment in subsidiaries	3,326		3,225
Net deferred income tax asset	(93)		(94)
Intercompany receivable	0		0
Other	10		26
Total assets	3,291		3,187
Liabilities and shareholders’ equity
Long-term debt	424		423
Intercompany payable	0		0
Other	1		15
Total liabilities	425		438
Total shareholders' equity	2,866		2,749
Total liabilities and shareholders' equity	3,291		3,187
Other Subsidiaries
Assets
Total investment portfolio and cash	11,012		11,233
Investment in subsidiaries	0		3,524
Premiums Receivable, at Carrying Value	1,091		1,147
Ceded unearned premium reserve	1,494		1,550
Deferred acquisition costs	185		190
Reinsurance recoverable on unpaid losses	205		223
Credit Risk Derivative Assets, at Fair Value	640		553
Net deferred income tax asset	943		789
Intercompany receivable	173		173
Financial guaranty variable interest entities’ assets, at fair value	2,813		2,688
Other	961		816
Total assets	19,517		22,886
Liabilities and shareholders’ equity
Unearned premium reserves	5,913		6,168
Loss and loss adjustment expense reserve	698		778
Long-term debt	60		66
Intercompany payable	300		300
Credit derivative liabilities	3,033		2,346
Financial guaranty variable interest entities' liabilities, at fair value	3,178		3,141
Other	838		803
Total liabilities	14,020		13,602
Total shareholders' equity	5,497		9,284
Total liabilities and shareholders' equity	19,517		22,886
Consolidating Adjustments
Assets
Total investment portfolio and cash	(300)		(300)
Investment in subsidiaries	(11,639)		(15,441)
Premiums Receivable, at Carrying Value	(135)		(142)
Ceded unearned premium reserve	(959)		(989)
Deferred acquisition costs	(69)		(74)
Reinsurance recoverable on unpaid losses	(149)		(165)
Credit Risk Derivative Assets, at Fair Value	(515)		(412)
Net deferred income tax asset	(26)		(22)
Intercompany receivable	(173)		(173)
Financial guaranty variable interest entities’ assets, at fair value	0		0
Other	(165)		(165)
Total assets	(14,130)		(17,883)
Liabilities and shareholders’ equity
Unearned premium reserves	(931)		(961)
Loss and loss adjustment expense reserve	(166)		(177)
Long-term debt	0		0
Intercompany payable	(473)		(473)
Credit derivative liabilities	(515)		(412)
Financial guaranty variable interest entities' liabilities, at fair value	0		0
Other	(296)		(303)
Total liabilities	(2,381)		(2,326)
Total shareholders' equity	(11,749)		(15,557)
Total liabilities and shareholders' equity	$ (14,130)		$ (17,883)

[1] )Excludes $28 million and $33 million as of March 31, 2013 and March 31, 2012, respectively, related to consolidated FG VIEs.