Parent Company - Condensed Statements of Operations and Comprehensive Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Condensed Income Statements, Captions [Line Items]
Net investment income	$ 269	$ 297	$ 378
Total revenues	848	1,115	963
Other expenses	179	197	125
Total expenses	465	729	503
Income (loss) before income taxes and equity in earnings of investees	383	386	460
Equity in earnings of investees	94	27	4
Net income (loss) attributable to Assured Guaranty Ltd.	389	362	402
Other comprehensive income (loss)	(198)	156	249
Comprehensive income (loss) attributable to Assured Guaranty Ltd.	191	518	651
Assured Guaranty Ltd. (Parent)
Condensed Income Statements, Captions [Line Items]
Net investment income	1	0	0
Total revenues	1	0	0
Other expenses	35	34	31
Total expenses	35	34	31
Income (loss) before income taxes and equity in earnings of investees	(34)	(34)	(31)
Equity in earnings of investees	423	396	433
Net income (loss) attributable to Assured Guaranty Ltd.	389	362	402
Other comprehensive income (loss)	(198)	156	249
Comprehensive income (loss) attributable to Assured Guaranty Ltd.	$ 191	$ 518	$ 651