Subsidiary Information - Condensed Consolidating Statement of Operations (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenues
Net earned premiums	$ 136	$ 162	$ 281	$ 326
Net investment income	99	101	200	223
Net realized investment gains (losses)	(2)	15	(7)	47
Net change in fair value of credit derivatives	48	(6)	82	48
Bargain purchase gain and settlement of pre-existing relationships	0	0	0	58
Other	(60)	36	(42)	133
Total revenues	221	308	514	835
Expenses
Loss and LAE	44	72	26	131
Amortization of deferred acquisition costs	4	4	9	8
Interest expense	24	25	48	49
Other operating expenses	62	57	127	125
Total expenses	134	158	210	313
Income (loss) before income taxes	87	150	304	522
Total (provision) benefit for income taxes	(12)	3	(32)	(52)
Equity in net earnings of subsidiaries	0	0	0	0
Net income (loss)	75	153	272	470
Less: noncontrolling interest	0	0	0	0
Net income (loss)	75	153	272	470
Comprehensive income (loss)	13	262	84	636
Reportable Legal Entities [Member] | Assured Guaranty Ltd. (Parent) [Member]
Revenues
Net earned premiums	0	0	0	0
Net investment income	0	0	0	0
Net realized investment gains (losses)	0	0	0	0
Net change in fair value of credit derivatives	0	0	0	0
Bargain purchase gain and settlement of pre-existing relationships				0
Other	3	2	6	5
Total revenues	3	2	6	5
Expenses
Loss and LAE	0	0	0	0
Amortization of deferred acquisition costs	0	0	0	0
Interest expense	0	0	0	0
Other operating expenses	10	10	20	20
Total expenses	10	10	20	20
Income (loss) before income taxes	(7)	(8)	(14)	(15)
Total (provision) benefit for income taxes	0	0	0	0
Equity in net earnings of subsidiaries	82	161	286	485
Net income (loss)	75	153	272	470
Less: noncontrolling interest	0	0	0	0
Net income (loss)	75	153	272	470
Comprehensive income (loss)	13	262	84	636
Reportable Legal Entities [Member] | Issuer Subsidiary [Member] | AGUS [Member]
Revenues
Net earned premiums	0	0	0	0
Net investment income	2	1	4	1
Net realized investment gains (losses)	0	0	0	0
Net change in fair value of credit derivatives	0	0	0	0
Bargain purchase gain and settlement of pre-existing relationships				0
Other	0	0	0	0
Total revenues	2	1	4	1
Expenses
Loss and LAE	0	0	0	0
Amortization of deferred acquisition costs	0	0	0	0
Interest expense	12	12	24	24
Other operating expenses	0	1	3	7
Total expenses	12	13	27	31
Income (loss) before income taxes	(10)	(12)	(23)	(30)
Total (provision) benefit for income taxes	2	3	5	9
Equity in net earnings of subsidiaries	64	138	225	337
Net income (loss)	56	129	207	316
Less: noncontrolling interest	0	0	0	0
Net income (loss)	56	129	207	316
Comprehensive income (loss)	7	224	74	468
Reportable Legal Entities [Member] | Issuer Subsidiary [Member] | AGMH [Member]
Revenues
Net earned premiums	0	0	0	0
Net investment income	0	0	0	0
Net realized investment gains (losses)	0	0	0	0
Net change in fair value of credit derivatives	0	0	0	0
Bargain purchase gain and settlement of pre-existing relationships				0
Other	0	0	0	0
Total revenues	0	0	0	0
Expenses
Loss and LAE	0	0	0	0
Amortization of deferred acquisition costs	0	0	0	0
Interest expense	14	14	27	27
Other operating expenses	1	0	1	1
Total expenses	15	14	28	28
Income (loss) before income taxes	(15)	(14)	(28)	(28)
Total (provision) benefit for income taxes	3	6	6	11
Equity in net earnings of subsidiaries	9	118	111	254
Net income (loss)	(3)	110	89	237
Less: noncontrolling interest	0	0	0	0
Net income (loss)	(3)	110	89	237
Comprehensive income (loss)	(53)	124	(7)	316
Reportable Legal Entities [Member] | Other Entities [Member]
Revenues
Net earned premiums	139	166	288	333
Net investment income	100	101	202	224
Net realized investment gains (losses)	(2)	30	(7)	62
Net change in fair value of credit derivatives	48	(6)	82	48
Bargain purchase gain and settlement of pre-existing relationships				58
Other	(9)	83	64	225
Total revenues	276	374	629	950
Expenses
Loss and LAE	46	40	30	51
Amortization of deferred acquisition costs	5	6	11	11
Interest expense	2	3	5	5
Other operating expenses	95	89	200	195
Total expenses	148	138	246	262
Income (loss) before income taxes	128	236	383	688
Total (provision) benefit for income taxes	(20)	(24)	(45)	(100)
Equity in net earnings of subsidiaries	6	6	13	14
Net income (loss)	114	218	351	602
Less: noncontrolling interest	6	6	13	14
Net income (loss)	108	212	338	588
Comprehensive income (loss)	52	293	163	730
Consolidation, Eliminations [Member]
Revenues
Net earned premiums	(3)	(4)	(7)	(7)
Net investment income	(3)	(1)	(6)	(2)
Net realized investment gains (losses)	0	(15)	0	(15)
Net change in fair value of credit derivatives	0	0	0	0
Bargain purchase gain and settlement of pre-existing relationships				0
Other	(54)	(49)	(112)	(97)
Total revenues	(60)	(69)	(125)	(121)
Expenses
Loss and LAE	(2)	32	(4)	80
Amortization of deferred acquisition costs	(1)	(2)	(2)	(3)
Interest expense	(4)	(4)	(8)	(7)
Other operating expenses	(44)	(43)	(97)	(98)
Total expenses	(51)	(17)	(111)	(28)
Income (loss) before income taxes	(9)	(52)	(14)	(93)
Total (provision) benefit for income taxes	3	18	2	28
Equity in net earnings of subsidiaries	(161)	(423)	(635)	(1,090)
Net income (loss)	(167)	(457)	(647)	(1,155)
Less: noncontrolling interest	(6)	(6)	(13)	(14)
Net income (loss)	(161)	(451)	(634)	(1,141)
Comprehensive income (loss)	$ (6)	$ (641)	$ (230)	$ (1,514)