Subsidiary Information - Condensed Consolidating Statement of Operations (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Revenues
Net earned premiums	$ 186	$ 231	$ 512	$ 628
Net investment income	99	94	322	291
Net realized investment gains (losses)	7	(2)	54	(5)
Net change in fair value of credit derivatives:
Realized gains (losses) and other settlements	(1)	15	19	47
Net unrealized gains (losses)	59	6	87	(23)
Net change in fair value of credit derivatives	58	21	106	24
Bargain purchase gain and settlement of pre-existing relationships	0	259	58	259
Other	273	(37)	406	10
Total revenues	623	566	1,458	1,207
Expenses
Loss and LAE	223	(9)	354	183
Amortization of deferred acquisition costs	5	4	13	13
Interest expense	24	26	73	77
Other operating expenses	58	65	183	188
Total expenses	310	86	623	461
Income (loss) before income taxes	313	480	835	746
Total (provision) benefit for income taxes	(105)	(1)	(157)	(62)
Equity in net earnings of subsidiaries	0	0	0	0
Net income (loss)	208	479	678	684
Less: noncontrolling interest	0	0	0	0
Net income (loss)	208	479	678	684
Comprehensive income (loss)	219	454	855	805
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	0	0
Other	3	0	8	0
Total revenues	3	0	8	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	7	30	23
Total expenses	10	7	30	23
Income (loss) before income taxes	(7)	(7)	(22)	(23)
Total (provision) benefit for income taxes	0	0	0	0
Equity in net earnings of subsidiaries	215	486	700	707
Net income (loss)	208	479	678	684
Less: noncontrolling interest	0	0	0	0
Net income (loss)	208	479	678	684
Comprehensive income (loss)	219	454	855	805
Reportable Legal Entities [Member] | Issuer Subsidiary [Member] | AGUS [Member]
Revenues
Net earned premiums	0	0	0	0
Net investment income	0	0	1	0
Net realized investment gains (losses)	0	3	0	3
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	0	0
Other	0	0	0	0
Total revenues	0	3	1	3
Expenses
Loss and LAE	0	0	0	0
Amortization of deferred acquisition costs	0	0	0	0
Interest expense	12	13	36	39
Other operating expenses	1	1	8	1
Total expenses	13	14	44	40
Income (loss) before income taxes	(13)	(11)	(43)	(37)
Total (provision) benefit for income taxes	4	4	13	13
Equity in net earnings of subsidiaries	237	433	574	623
Net income (loss)	228	426	544	599
Less: noncontrolling interest	0	0	0	0
Net income (loss)	228	426	544	599
Comprehensive income (loss)	237	414	705	660
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	0	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	13	13	40	40
Other operating expenses	0	1	1	2
Total expenses	13	14	41	42
Income (loss) before income taxes	(13)	(14)	(41)	(42)
Total (provision) benefit for income taxes	4	5	15	15
Equity in net earnings of subsidiaries	178	82	422	272
Net income (loss)	169	73	396	245
Less: noncontrolling interest	0	0	0	0
Net income (loss)	169	73	396	245
Comprehensive income (loss)	178	51	484	261
Reportable Legal Entities [Member] | Other Entities [Member]
Revenues
Net earned premiums	190	239	523	653
Net investment income	101	95	325	293
Net realized investment gains (losses)	(9)	(2)	53	(4)
Net change in fair value of credit derivatives:
Realized gains (losses) and other settlements	(1)	15	19	47
Net unrealized gains (losses)	59	6	87	(23)
Net change in fair value of credit derivatives	58	21	106	24
Bargain purchase gain and settlement of pre-existing relationships		257	58	257
Other	302	(37)	527	10
Total revenues	642	573	1,592	1,233
Expenses
Loss and LAE	250	(15)	301	182
Amortization of deferred acquisition costs	8	9	19	23
Interest expense	3	3	8	8
Other operating expenses	91	58	286	165
Total expenses	352	55	614	378
Income (loss) before income taxes	290	518	978	855
Total (provision) benefit for income taxes	(94)	(13)	(194)	(94)
Equity in net earnings of subsidiaries	8	11	22	34
Net income (loss)	204	516	806	795
Less: noncontrolling interest	8	11	22	34
Net income (loss)	196	505	784	761
Comprehensive income (loss)	274	497	1,004	923
Consolidation, Eliminations [Member]
Revenues
Net earned premiums	(4)	(8)	(11)	(25)
Net investment income	(2)	(1)	(4)	(2)
Net realized investment gains (losses)	16	(3)	1	(4)
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		2	0	2
Other	(32)	0	(129)	0
Total revenues	(22)	(10)	(143)	(29)
Expenses
Loss and LAE	(27)	6	53	1
Amortization of deferred acquisition costs	(3)	(5)	(6)	(10)
Interest expense	(4)	(3)	(11)	(10)
Other operating expenses	(44)	(2)	(142)	(3)
Total expenses	(78)	(4)	(106)	(22)
Income (loss) before income taxes	56	(6)	(37)	(7)
Total (provision) benefit for income taxes	(19)	3	9	4
Equity in net earnings of subsidiaries	(638)	(1,012)	(1,718)	(1,636)
Net income (loss)	(601)	(1,015)	(1,746)	(1,639)
Less: noncontrolling interest	(8)	(11)	(22)	(34)
Net income (loss)	(593)	(1,004)	(1,724)	(1,605)
Comprehensive income (loss)	$ (689)	$ (962)	$ (2,193)	$ (1,844)