Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 401	$ 521	$ 730
Change in net unrealized gains (losses) on:
Investments with no other-than-temporary impairment, net of tax provision (benefit) of $46, $(32) and $27	293	(215)	64
Investments with other-than-temporary impairment, net of tax provision (benefit) of $(14), $(8) and $46	(46)	(26)	89
Change in net unrealized gains (losses) on investments	247	(241)	153
Change in net unrealized gains (losses) on financial guaranty variable interest entities' liabilities with recourse, net of tax	4	2	0
Other, net of tax provision (benefit) of $0, $(2) and $2	(2)	(8)	14
Other comprehensive income (loss)	249	(247)	167
Comprehensive income (loss)	650	274	897
Less: Comprehensive income (loss) attributable to noncontrolling interests	(1)	0	0
Comprehensive income (loss) attributable to Assured Guaranty Ltd.	$ 651	$ 274	$ 897