Subsidiary Information - Condensed Consolidating Statement of Operations (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Revenues
Net earned premiums	$ 162	$ 214	$ 326	$ 397
Net investment income	101	98	223	197
Net realized investment gains (losses)	15	10	47	(3)
Net change in fair value of credit derivatives:
Realized gains (losses) and other settlements	5	24	20	32
Net unrealized gains (losses)	(11)	39	28	(29)
Net change in fair value of credit derivatives	(6)	63	48	3
Bargain purchase gain and settlement of pre-existing relationships	0	0	58	0
Other	36	11	133	47
Total revenues	308	396	835	641
Expenses
Loss and LAE	72	102	131	192
Amortization of deferred acquisition costs	4	5	8	9
Interest expense	25	25	49	51
Other operating expenses	57	63	125	123
Total expenses	158	195	313	375
Income (loss) before income taxes	150	201	522	266
Total (provision) benefit for income taxes	3	(55)	(52)	(61)
Equity in net earnings of subsidiaries	0	0	0	0
Net income (loss)	153	146	470	205
Less: noncontrolling interest	0	0	0	0
Net income (loss)	153	146	470	205
Comprehensive income (loss)	262	210	636	351
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:
Realized gains (losses) and other settlements	0	0	0	0
Net unrealized 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	2	0	5	0
Total revenues	2	0	5	0
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	8	20	16
Total expenses	10	8	20	16
Income (loss) before income taxes	(8)	(8)	(15)	(16)
Total (provision) benefit for income taxes	0	0	0	0
Equity in net earnings of subsidiaries	161	154	485	221
Net income (loss)	153	146	470	205
Less: noncontrolling interest	0	0	0	0
Net income (loss)	153	146	470	205
Comprehensive income (loss)	262	210	636	351
Reportable Legal Entities [Member] | Issuer Subsidiary [Member] | AGUS [Member]
Revenues
Net earned premiums	0	0	0	0
Net investment income	1	0	1	0
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
Net unrealized 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	1	0	1	0
Expenses
Loss and LAE	0	0	0	0
Amortization of deferred acquisition costs	0	0	0	0
Interest expense	12	13	24	26
Other operating expenses	1	0	7	0
Total expenses	13	13	31	26
Income (loss) before income taxes	(12)	(13)	(30)	(26)
Total (provision) benefit for income taxes	3	4	9	9
Equity in net earnings of subsidiaries	138	140	337	190
Net income (loss)	129	131	316	173
Less: noncontrolling interest	0	0	0	0
Net income (loss)	129	131	316	173
Comprehensive income (loss)	224	166	468	246
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:
Realized gains (losses) and other settlements	0	0	0	0
Net unrealized 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	0	0	1	1
Total expenses	14	14	28	28
Income (loss) before income taxes	(14)	(14)	(28)	(28)
Total (provision) benefit for income taxes	6	5	11	10
Equity in net earnings of subsidiaries	118	114	254	190
Net income (loss)	110	105	237	172
Less: noncontrolling interest	0	0	0	0
Net income (loss)	110	105	237	172
Comprehensive income (loss)	124	125	316	210
Reportable Legal Entities [Member] | Other Entities [Member]
Revenues
Net earned premiums	166	222	333	414
Net investment income	101	98	224	198
Net realized investment gains (losses)	30	10	62	(2)
Net change in fair value of credit derivatives:
Realized gains (losses) and other settlements	5	24	20	32
Net unrealized gains (losses)	(11)	39	28	(29)
Net change in fair value of credit derivatives	(6)	63	48	3
Bargain purchase gain and settlement of pre-existing relationships			58
Other	83	11	225	47
Total revenues	374	404	950	660
Expenses
Loss and LAE	40	104	51	197
Amortization of deferred acquisition costs	6	7	11	14
Interest expense	3	2	5	5
Other operating expenses	89	55	195	107
Total expenses	138	168	262	323
Income (loss) before income taxes	236	236	688	337
Total (provision) benefit for income taxes	(24)	(65)	(100)	(81)
Equity in net earnings of subsidiaries	6	14	14	23
Net income (loss)	218	185	602	279
Less: noncontrolling interest	6	14	14	23
Net income (loss)	212	171	588	256
Comprehensive income (loss)	293	248	730	426
Consolidation, Eliminations [Member]
Revenues
Net earned premiums	(4)	(8)	(7)	(17)
Net investment income	(1)	0	(2)	(1)
Net realized investment gains (losses)	(15)	0	(15)	(1)
Net change in fair value of credit derivatives:
Realized gains (losses) and other settlements	0	0	0	0
Net unrealized 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	(49)	0	(97)	0
Total revenues	(69)	(8)	(121)	(19)
Expenses
Loss and LAE	32	(2)	80	(5)
Amortization of deferred acquisition costs	(2)	(2)	(3)	(5)
Interest expense	(4)	(4)	(7)	(7)
Other operating expenses	(43)	0	(98)	(1)
Total expenses	(17)	(8)	(28)	(18)
Income (loss) before income taxes	(52)	0	(93)	(1)
Total (provision) benefit for income taxes	18	1	28	1
Equity in net earnings of subsidiaries	(423)	(422)	(1,090)	(624)
Net income (loss)	(457)	(421)	(1,155)	(624)
Less: noncontrolling interest	(6)	(14)	(14)	(23)
Net income (loss)	(451)	(407)	(1,141)	(601)
Comprehensive income (loss)	$ (641)	$ (539)	$ (1,514)	$ (882)