Subsidiary Information (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Revenues
Net earned premiums	$ 222	$ 211	$ 635	$ 695
Net investment income	102	95	301	295
Net realized investment gains (losses)	2	(11)	0	(13)
Net change in fair value of credit derivatives:
Realized gains (losses) and other settlements	2	0	(78)	25
Unrealized Gains (Losses)	(38)	1,156	(388)	830
Net change in fair value of credit derivatives	(36)	1,156	(466)	855
Equity in earnings of subsidiaries	0	0	0	0
Other	52	(106)	274	(92)
Total revenues	342	1,345	744	1,740
Expenses
Loss and loss adjustment expenses	90	215	459	313
Amortization of deferred acquisition costs	4	4	14	13
Interest expense	21	25	71	74
Other operating expenses	48	46	163	163
Total expenses	163	290	707	563
Income (loss) before income taxes	179	1,055	37	1,177
Total provision (benefit) for income taxes	37	294	1	320
Net income (loss)	142	761	36	857
Comprehensive income (loss)	243	882	199	1,072
Assured Guaranty Ltd. (Parent)
Revenues
Net investment income	0	0	0	0
Net realized investment gains (losses)	0	0	0	0
Net change in fair value of credit derivatives:
Equity in earnings of subsidiaries	146	766	52	876
Other	0	0	0	0
Total revenues	146	766	52	876
Expenses
Interest expense	0	0	0	0
Other operating expenses	4	5	16	19
Total expenses	4	5	16	19
Income (loss) before income taxes	142	761	36	857
Total provision (benefit) for income taxes	0	0	0	0
Net income (loss)	142	761	36	857
Comprehensive income (loss)	243	882	199	1,072
AGUS (Issuer)
Revenues
Net investment income	0	0	0	0
Net realized investment gains (losses)	0	0	0	0
Net change in fair value of credit derivatives:
Equity in earnings of subsidiaries	105	586	112	715
Other	0	0	0	0
Total revenues	105	586	112	715
Expenses
Interest expense	7	10	27	30
Other operating expenses	0	1	1	1
Total expenses	7	11	28	31
Income (loss) before income taxes	98	575	84	684
Total provision (benefit) for income taxes	(3)	(4)	(10)	(11)
Net income (loss)	101	579	94	695
Comprehensive income (loss)	175	664	212	867
AGMH (Issuer)
Revenues
Net investment income	0	0	1	0
Net realized investment gains (losses)	0	0	0	0
Net change in fair value of credit derivatives:
Equity in earnings of subsidiaries	157	15	319	352
Other	0	0	0	0
Total revenues	157	15	320	352
Expenses
Interest expense	13	13	40	40
Other operating expenses	1	0	1	1
Total expenses	14	13	41	41
Income (loss) before income taxes	143	2	279	311
Total provision (benefit) for income taxes	(5)	(5)	(14)	(14)
Net income (loss)	148	7	293	325
Comprehensive income (loss)	190	55	364	426
Other Subsidiaries
Revenues
Net earned premiums	219	208	625	687
Net investment income	107	99	313	306
Net realized investment gains (losses)	2	(11)	0	(13)
Net change in fair value of credit derivatives:
Realized gains (losses) and other settlements	2	0	(78)	25
Unrealized Gains (Losses)	(38)	1,156	(388)	830
Net change in fair value of credit derivatives	(36)	1,156	(466)	855
Equity in earnings of subsidiaries	100	579	94	695
Other	53	(106)	276	(90)
Total revenues	445	1,925	842	2,440
Expenses
Loss and loss adjustment expenses	90	219	461	314
Amortization of deferred acquisition costs	6	7	24	28
Interest expense	6	6	17	15
Other operating expenses	44	43	149	147
Total expenses	146	275	651	504
Income (loss) before income taxes	299	1,650	191	1,936
Total provision (benefit) for income taxes	42	296	17	335
Net income (loss)	257	1,354	174	1,601
Comprehensive income (loss)	432	1,560	455	1,988
Consolidating Adjustments
Revenues
Net earned premiums	3	3	10	8
Net investment income	(5)	(4)	(13)	(11)
Net realized investment gains (losses)	0	0	0	0
Net change in fair value of credit derivatives:
Realized gains (losses) and other settlements	0	0	0	0
Unrealized Gains (Losses)	0	0	0	0
Net change in fair value of credit derivatives	0	0	0	0
Equity in earnings of subsidiaries	(508)	(1,946)	(577)	(2,638)
Other	(1)	0	(2)	(2)
Total revenues	(511)	(1,947)	(582)	(2,643)
Expenses
Loss and loss adjustment expenses	0	(4)	(2)	(1)
Amortization of deferred acquisition costs	(2)	(3)	(10)	(15)
Interest expense	(5)	(4)	(13)	(11)
Other operating expenses	(1)	(3)	(4)	(5)
Total expenses	(8)	(14)	(29)	(32)
Income (loss) before income taxes	(503)	(1,933)	(553)	(2,611)
Total provision (benefit) for income taxes	3	7	8	10
Net income (loss)	(506)	(1,940)	(561)	(2,621)
Comprehensive income (loss)	$ (797)	$ (2,279)	$ (1,031)	$ (3,281)