| Cover Page Cover Page | May 06, 2021 |
| Entity Information [Line Items] | |
| Document Type | 8-K |
| Document Period End Date | May 19, 2021 |
| Entity Registrant Name | ASSURED GUARANTY LTD. |
| Entity Incorporation, State or Country Code | D0 |
| Entity File Number | 001-32141 |
| 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 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| Amendment Flag | false |
| Entity Central Index Key | 0001273813 |
| Common Shares | New York Stock Exchange | |
| Entity Information [Line Items] | |
| Title of 12(b) Security | Common Shares |
| Trading Symbol | AGO |
| Security Exchange Name | NYSE |
| Assured Guaranty Municipal Holdings Inc. 6-7/8% $100,000,000 Quarterly Interest Bonds due 2101 (and the related guarantee of Registrant) | New York Stock Exchange | |
| Entity Information [Line Items] | |
| Title of 12(b) Security | Assured Guaranty Municipal Holdings Inc. 6-7/8% $100,000,000 Quarterly Interest Bonds due 2101 (and the related guarantee of Registrant) |
| Trading Symbol | AGO PRB |
| Security Exchange Name | NYSE |
| Assured Guaranty Municipal Holdings Inc. 6.25% $230,000,000 Quarterly Interest Bonds due 2102 (and the related guarantee of Registrant) | New York Stock Exchange | |
| Entity Information [Line Items] | |
| Title of 12(b) Security | Assured Guaranty Municipal Holdings Inc. 6.25% $230,000,000 Quarterly Interest Bonds due 2102 (and the related guarantee of Registrant) |
| Trading Symbol | AGO PRE |
| Security Exchange Name | NYSE |
| Assured Guaranty Municipal Holdings Inc. 5.60% $100,000,000 Quarterly Interest Bonds due 2103 (and the related guarantee of Registrant) | New York Stock Exchange | |
| Entity Information [Line Items] | |
| Title of 12(b) Security | Assured Guaranty Municipal Holdings Inc. 5.60% $100,000,000 Quarterly Interest Bonds due 2103 (and the related guarantee of Registrant) |
| Trading Symbol | AGO PRF |
| Security Exchange Name | NYSE |
| Assured Guaranty US Holdings Inc. 5.000% $500,000,000 Senior Notes due 2024 (and the related guarantee of Registrant) | New York Stock Exchange | |
| Entity Information [Line Items] | |
| Title of 12(b) Security | Assured Guaranty US Holdings Inc. 5.000% $500,000,000 Senior Notes due 2024 (and the related guarantee of Registrant) |
| Trading Symbol | AGO 24 |
| Security Exchange Name | NYSE |
