Cover Page - USD ($)	12 Months Ended
	Dec. 31, 2019	Feb. 25, 2020	Jun. 28, 2019
Cover page.
Document Type	10-K
Document Period End Date	Dec. 31, 2019
Document Annual Report	true
Document Transition Report	false
Entity File Number	001-32141
Entity Registrant Name	ASSURED GUARANTY LTD
Entity Incorporation, State or Country Code	D0
Entity Tax Identification Number	98-0429991
Entity Address, Address Line One	30 Woodbourne Avenue
Entity Address, City or Town	Hamilton
Entity Address, Postal Zip Code	HM 08
Entity Address, Country	BM
City Area Code	441
Local Phone Number	279-5700
Title of 12(b) Security	Common Shares
Trading Symbol	AGO
Security Exchange Name	NYSE
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Public Float			$ 4,084,346,347
Entity Common Stock, Shares Outstanding		92,581,878
Entity Central Index Key	0001273813
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY