Subsidiary Information - Condensed Consolidating Statement of Operations (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues
Net earned premiums	$ 178	$ 186	$ 162	$ 164	$ 236	$ 231	$ 214	$ 183	$ 690	$ 864	$ 766
Net investment income	96	99	101	122	117	94	98	99	418	408	423
Net realized investment gains (losses)	(14)	7	15	32	(24)	(2)	10	(13)	40	(29)	(26)
Net change in fair value of credit derivatives:
Realized gains (losses) and other settlements									(10)	29	(18)
Net unrealized gains (losses)									121	69	746
Net change in fair value of credit derivatives	5	58	(6)	54	74	21	63	(60)	111	98	728
Bargain purchase gain and settlement of pre-existing relationships	0	0	0	58	0	259	0	0	58	259	214
Other									422	77	102
Total revenues									1,739	1,677	2,207
Expenses
Loss and LAE	34	223	72	59	112	(9)	102	90	388	295	424
Amortization of DAC	6	5	4	4	5	4	5	4	19	18	20
Interest expense	24	24	25	24	25	26	25	26	97	102	101
Other operating expenses	61	58	57	68	57	65	63	60	244	245	231
Total expenses									748	660	776
Income (loss) before income taxes	156	313	150	372	271	480	201	65	991	1,017	1,431
Total (provision) benefit for income taxes	(104)	(105)	3	(55)	(74)	(1)	(55)	(6)	(261)	(136)	(375)
Equity in net earnings of subsidiaries									0	0	0
Net income (loss)									730	881	1,056
Less: noncontrolling interest									0	0	0
Net income (loss)	$ 52	$ 208	$ 153	$ 317	$ 197	$ 479	$ 146	$ 59	730	881	1,056
Comprehensive income (loss)									897	793	923
Reportable Legal Entities [Member] | Assured Guaranty Ltd. (Parent) [Member]
Revenues
Net earned premiums									0	0	0
Net investment income									0	0	0
Net realized investment gains (losses)									0	0	0
Net change in fair value of credit derivatives:
Realized gains (losses) and other settlements									0	0	0
Net unrealized gains (losses)									0	0	0
Net change in fair value of credit derivatives									0	0	0
Bargain purchase gain and settlement of pre-existing relationships									0	0	0
Other									10	0	0
Total revenues									10	0	0
Expenses
Loss and LAE									0	0	0
Amortization of DAC									0	0	0
Interest expense									0	0	0
Other operating expenses									38	29	30
Total expenses									38	29	30
Income (loss) before income taxes									(28)	(29)	(30)
Total (provision) benefit for income taxes									0	0	0
Equity in net earnings of subsidiaries									758	910	1,086
Net income (loss)									730	881	1,056
Less: noncontrolling interest									0	0	0
Net income (loss)									730	881	1,056
Comprehensive income (loss)									897	793	923
Reportable Legal Entities [Member] | AGUS (Issuer) [Member]
Revenues
Net earned premiums									0	0	0
Net investment income									2	0	1
Net realized investment gains (losses)									0	2	0
Net change in fair value of credit derivatives:
Realized gains (losses) and other settlements									0	0	0
Net unrealized gains (losses)									0	0	0
Net change in fair value of credit derivatives									0	0	0
Bargain purchase gain and settlement of pre-existing relationships									0	0	0
Other									0	0	0
Total revenues									2	2	1
Expenses
Loss and LAE									0	0	0
Amortization of DAC									0	0	0
Interest expense									47	52	52
Other operating expenses									12	2	1
Total expenses									59	54	53
Income (loss) before income taxes									(57)	(52)	(52)
Total (provision) benefit for income taxes									17	18	18
Equity in net earnings of subsidiaries									636	794	923
Net income (loss)									596	760	889
Less: noncontrolling interest									0	0	0
Net income (loss)									596	760	889
Comprehensive income (loss)									754	685	787
Reportable Legal Entities [Member] | AGMH (Issuer) [Member]
Revenues
Net earned premiums									0	0	0
Net investment income									0	0	0
Net realized investment gains (losses)									0	0	1
Net change in fair value of credit derivatives:
Realized gains (losses) and other settlements									0	0	0
Net unrealized gains (losses)									0	0	0
Net change in fair value of credit derivatives									0	0	0
Bargain purchase gain and settlement of pre-existing relationships									0	0	0
Other									0	0	0
Total revenues									0	0	1
Expenses
Loss and LAE									0	0	0
Amortization of DAC									0	0	0
Interest expense									54	54	54
Other operating expenses									1	2	1
Total expenses									55	56	55
Income (loss) before income taxes									(55)	(56)	(54)
Total (provision) benefit for income taxes									54	20	19
Equity in net earnings of subsidiaries									395	274	464
Net income (loss)									394	238	429
Less: noncontrolling interest									0	0	0
Net income (loss)									394	238	429
Comprehensive income (loss)									482	144	348
Reportable Legal Entities [Member] | Other Entities [Member]
Revenues
Net earned premiums									728	892	783
Net investment income									427	412	432
Net realized investment gains (losses)									45	(28)	(19)
Net change in fair value of credit derivatives:
Realized gains (losses) and other settlements									(10)	29	(18)
Net unrealized gains (losses)									121	69	773
Net change in fair value of credit derivatives									111	98	755
Bargain purchase gain and settlement of pre-existing relationships									58	257	54
Other									608	78	102
Total revenues									1,977	1,709	2,107
Expenses
Loss and LAE									327	296	434
Amortization of DAC									26	30	29
Interest expense									11	10	14
Other operating expenses									394	217	202
Total expenses									758	553	679
Income (loss) before income taxes									1,219	1,156	1,428
Total (provision) benefit for income taxes									(359)	(175)	(365)
Equity in net earnings of subsidiaries									32	44	39
Net income (loss)									892	1,025	1,102
Less: noncontrolling interest									32	44	39
Net income (loss)									860	981	1,063
Comprehensive income (loss)									1,084	953	967
Consolidation, Eliminations [Member]
Revenues
Net earned premiums									(38)	(28)	(17)
Net investment income									(11)	(4)	(10)
Net realized investment gains (losses)									(5)	(3)	(8)
Net change in fair value of credit derivatives:
Realized gains (losses) and other settlements									0	0	0
Net unrealized gains (losses)									0	0	(27)
Net change in fair value of credit derivatives									0	0	(27)
Bargain purchase gain and settlement of pre-existing relationships									0	2	160
Other									(196)	(1)	0
Total revenues									(250)	(34)	98
Expenses
Loss and LAE									61	(1)	(10)
Amortization of DAC									(7)	(12)	(9)
Interest expense									(15)	(14)	(19)
Other operating expenses									(201)	(5)	(3)
Total expenses									(162)	(32)	(41)
Income (loss) before income taxes									(88)	(2)	139
Total (provision) benefit for income taxes									27	1	(47)
Equity in net earnings of subsidiaries									(1,821)	(2,022)	(2,512)
Net income (loss)									(1,882)	(2,023)	(2,420)
Less: noncontrolling interest									(32)	(44)	(39)
Net income (loss)									(1,850)	(1,979)	(2,381)
Comprehensive income (loss)									$ (2,320)	$ (1,782)	$ (2,102)