Subsidiary Information - Condensed Consolidating Statement of Operations (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Revenues
Net earned premiums	$ 145	$ 164
Net investment income	101	122
Net realized investment gains (losses)	(5)	32
Net change in fair value of credit derivatives:
Realized gains (losses) and other settlements	2	15
Net unrealized gains (losses)	32	39
Net change in fair value of credit derivatives	34	54
Bargain purchase gain and settlement of pre-existing relationships	0	58
Other	18	97
Total revenues	293	527
Expenses
Loss and LAE	(18)	59
Amortization of deferred acquisition costs	5	4
Interest expense	24	24
Other operating expenses	65	68
Total expenses	76	155
Income (loss) before income taxes	217	372
Total (provision) benefit for income taxes	(20)	(55)
Equity in net earnings of subsidiaries	0	0
Net income (loss)	197	317
Less: noncontrolling interest	0	0
Net income (loss)	197	317
Comprehensive income (loss)	71	374
Reportable Legal Entities [Member] | Assured Guaranty Ltd. (Parent) [Member]
Revenues
Net earned premiums	0	0
Net investment income	0	0
Net realized investment gains (losses)	0	0
Net change in fair value of credit derivatives:
Realized gains (losses) and other settlements	0	0
Net unrealized gains (losses)	0	0
Net change in fair value of credit derivatives	0	0
Bargain purchase gain and settlement of pre-existing relationships		0
Other	3	3
Total revenues	3	3
Expenses
Loss and LAE	0	0
Amortization of deferred acquisition costs	0	0
Interest expense	0	0
Other operating expenses	10	10
Total expenses	10	10
Income (loss) before income taxes	(7)	(7)
Total (provision) benefit for income taxes	0	0
Equity in net earnings of subsidiaries	204	324
Net income (loss)	197	317
Less: noncontrolling interest	0	0
Net income (loss)	197	317
Comprehensive income (loss)	71	374
Reportable Legal Entities [Member] | Issuer Subsidiary [Member] | AGUS [Member]
Revenues
Net earned premiums	0	0
Net investment income	2	0
Net realized investment gains (losses)	0	0
Net change in fair value of credit derivatives:
Realized gains (losses) and other settlements	0	0
Net unrealized gains (losses)	0	0
Net change in fair value of credit derivatives	0	0
Bargain purchase gain and settlement of pre-existing relationships		0
Other	0	0
Total revenues	2	0
Expenses
Loss and LAE	0	0
Amortization of deferred acquisition costs	0	0
Interest expense	12	12
Other operating expenses	3	6
Total expenses	15	18
Income (loss) before income taxes	(13)	(18)
Total (provision) benefit for income taxes	3	6
Equity in net earnings of subsidiaries	161	199
Net income (loss)	151	187
Less: noncontrolling interest	0	0
Net income (loss)	151	187
Comprehensive income (loss)	67	244
Reportable Legal Entities [Member] | Issuer Subsidiary [Member] | AGMH [Member]
Revenues
Net earned premiums	0	0
Net investment income	0	0
Net realized investment gains (losses)	0	0
Net change in fair value of credit derivatives:
Realized gains (losses) and other settlements	0	0
Net unrealized gains (losses)	0	0
Net change in fair value of credit derivatives	0	0
Bargain purchase gain and settlement of pre-existing relationships		0
Other	0	0
Total revenues	0	0
Expenses
Loss and LAE	0	0
Amortization of deferred acquisition costs	0	0
Interest expense	13	13
Other operating expenses	0	1
Total expenses	13	14
Income (loss) before income taxes	(13)	(14)
Total (provision) benefit for income taxes	3	5
Equity in net earnings of subsidiaries	102	136
Net income (loss)	92	127
Less: noncontrolling interest	0	0
Net income (loss)	92	127
Comprehensive income (loss)	46	192
Reportable Legal Entities [Member] | Other Entities [Member]
Revenues
Net earned premiums	149	167
Net investment income	102	123
Net realized investment gains (losses)	(5)	32
Net change in fair value of credit derivatives:
Realized gains (losses) and other settlements	2	15
Net unrealized gains (losses)	32	39
Net change in fair value of credit derivatives	34	54
Bargain purchase gain and settlement of pre-existing relationships		58
Other	73	142
Total revenues	353	576
Expenses
Loss and LAE	(16)	11
Amortization of deferred acquisition costs	6	5
Interest expense	3	2
Other operating expenses	105	106
Total expenses	98	124
Income (loss) before income taxes	255	452
Total (provision) benefit for income taxes	(25)	(76)
Equity in net earnings of subsidiaries	7	8
Net income (loss)	237	384
Less: noncontrolling interest	7	8
Net income (loss)	230	376
Comprehensive income (loss)	111	437
Consolidation, Eliminations [Member]
Revenues
Net earned premiums	(4)	(3)
Net investment income	(3)	(1)
Net realized investment gains (losses)	0	0
Net change in fair value of credit derivatives:
Realized gains (losses) and other settlements	0	0
Net unrealized gains (losses)	0	0
Net change in fair value of credit derivatives	0	0
Bargain purchase gain and settlement of pre-existing relationships		0
Other	(58)	(48)
Total revenues	(65)	(52)
Expenses
Loss and LAE	(2)	48
Amortization of deferred acquisition costs	(1)	(1)
Interest expense	(4)	(3)
Other operating expenses	(53)	(55)
Total expenses	(60)	(11)
Income (loss) before income taxes	(5)	(41)
Total (provision) benefit for income taxes	(1)	10
Equity in net earnings of subsidiaries	(474)	(667)
Net income (loss)	(480)	(698)
Less: noncontrolling interest	(7)	(8)
Net income (loss)	(473)	(690)
Comprehensive income (loss)	$ (224)	$ (873)