Condensed Consolidated Statements of Comprehensive Income (Loss) (unaudited) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 15	$ (58)
Change in net unrealized gains (losses) on:
Investments with no credit impairment, net of tax provision (benefit) of $(20) and $(27)	(119)	(162)
Investments with credit impairment, net of tax provision (benefit) of $(1) and $(13)	(6)	(52)
Change in net unrealized gains (losses) on investments	(125)	(214)
Change in net unrealized gains (losses) on financial guaranty variable interest entities' liabilities with recourse, net of tax	(1)	10
Other, net of tax provision (benefit)	1	0
Other comprehensive income (loss)	(125)	(204)
Comprehensive income (loss)	(110)	(262)
Less: Comprehensive income (loss) attributable to noncontrolling interests	4	(3)
Comprehensive income (loss) attributable to Assured Guaranty Ltd.	$ (114)	$ (259)