Segment Information - Reconciliation of Net Income (Loss) Attributable to AGL to Segment Adjusted Operating Income (Loss) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Segment Reporting Information [Line Items]
Total revenues	$ 872	$ 1,373	$ 723
Total expenses	446	733	536
Equity in earnings (losses) of investees	62	28	(39)
Less: Segment provision (benefit) for income taxes	96	(93)	11
Less: Noncontrolling interests	16	22	13
Net income (loss) attributable to Assured Guaranty Ltd.	376	739	124
Bermuda ETA	1	189	0
Subtotal
Segment Reporting Information [Line Items]
Total revenues	886	1,267	887
Total expenses	447	735	540
Equity in earnings (losses) of investees	62	28	(39)
Less: Segment provision (benefit) for income taxes	96	(110)	28
Less: Noncontrolling interests	16	22	13
Net income (loss) attributable to Assured Guaranty Ltd.	389	648	267
Realized gains (losses) on investments
Segment Reporting Information [Line Items]
Total revenues	9	(14)	(56)
Net income (loss) attributable to Assured Guaranty Ltd.	9	(14)	(56)
Non-credit impairment-related unrealized fair value gains (losses) on credit derivatives
Segment Reporting Information [Line Items]
Total revenues	13	104	(22)
Net income (loss) attributable to Assured Guaranty Ltd.	14	106	(18)
Fair value gains (losses) on CCS
Segment Reporting Information [Line Items]
Total revenues	(10)	(35)	24
Net income (loss) attributable to Assured Guaranty Ltd.	(10)	(35)	24
Foreign exchange gains (losses) on remeasurement of premiums receivable and loss and LAE reserves
Segment Reporting Information [Line Items]
Total revenues	(26)	51	(110)
Net income (loss) attributable to Assured Guaranty Ltd.	(26)	51	(110)
Tax effect
Segment Reporting Information [Line Items]
Less: Segment provision (benefit) for income taxes	0	(17)	17
Net income (loss) attributable to Assured Guaranty Ltd.	0	(17)	17
Operating segments
Segment Reporting Information [Line Items]
Total revenues	831	931	869
Total expenses	295	513	378
Equity in earnings (losses) of investees	104	87	(51)
Less: Segment provision (benefit) for income taxes	110	(119)	33
Less: Noncontrolling interests	0	0	0
Net income (loss) attributable to Assured Guaranty Ltd.	530	624	407
Operating segments | Insurance
Segment Reporting Information [Line Items]
Total revenues	821	855	757
Total expenses	289	435	259
Equity in earnings (losses) of investees	102	82	(51)
Less: Segment provision (benefit) for income taxes	109	(119)	34
Less: Noncontrolling interests	0	0	0
Net income (loss) attributable to Assured Guaranty Ltd.	525	621	413
Operating segments | Asset Management
Segment Reporting Information [Line Items]
Total revenues	10	76	112
Total expenses	6	78	119
Equity in earnings (losses) of investees	2	5	0
Less: Segment provision (benefit) for income taxes	1	0	(1)
Less: Noncontrolling interests	0	0	0
Net income (loss) attributable to Assured Guaranty Ltd.	5	3	(6)
Corporate division
Segment Reporting Information [Line Items]
Total revenues	17	275	4
Total expenses	169	216	143
Equity in earnings (losses) of investees	5	0	0
Less: Segment provision (benefit) for income taxes	(12)	14	(5)
Less: Noncontrolling interests	0	0	0
Net income (loss) attributable to Assured Guaranty Ltd.	(135)	45	(134)
Intersegment, other
Segment Reporting Information [Line Items]
Total revenues	38
Total expenses	(17)
Equity in earnings (losses) of investees	(47)
Less: Segment provision (benefit) for income taxes	(2)
Less: Noncontrolling interests	16
Net income (loss) attributable to Assured Guaranty Ltd.	(6)
Intersegment, other | Insurance
Segment Reporting Information [Line Items]
Total revenues	10	10	9
Intersegment, other | Asset Management
Segment Reporting Information [Line Items]
Total revenues	2	27	34
Other
Segment Reporting Information [Line Items]
Total revenues		61	14
Total expenses		6	19
Equity in earnings (losses) of investees		(59)	12
Less: Segment provision (benefit) for income taxes		(5)	0
Less: Noncontrolling interests		22	13
Net income (loss) attributable to Assured Guaranty Ltd.		(21)	(6)
Reconciling item
Segment Reporting Information [Line Items]
Total expenses	$ (1)	$ (2)	$ (4)