Condensed Consolidated Statements of Comprehensive Income (unaudited) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Statement of Comprehensive Income [Abstract]
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	$ (58)	$ 54
Change in net unrealized gains (losses) on:
Investments with no credit impairment recognized in the statement of operations, net of tax provision (benefit) of $(27) and $25	(162)	163
Investments with credit impairment recognized in the statement of operations, net of tax provision (benefit) of $(13) and $0	(52)	5
Change in net unrealized gains (losses) on investments	(214)	168
Change in net unrealized gains (losses) on financial guaranty variable interest entities' liabilities with recourse, net of tax	10	0
Other, net of tax provision (benefit) of $0 and $0	0	0
Other comprehensive income (loss)	(204)	168
Comprehensive income (loss)	(262)	222
Less: Comprehensive income (loss) attributable to noncontrolling interest	(3)	0
Comprehensive income (loss) attributable to Assured Guaranty Ltd.	$ (259)	$ 222

Other Comprehensive Income (Loss), Available-for-sale Securities, With Credit Impairment, Net of Tax

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Other Comprehensive Income (Loss), Available-for-sale Securities, Without Credit Impairment, Net of Tax

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Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax, Portion Attributable to Parent and Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax, Portion Attributable to Parent

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