Reinsurance - Narrative (Details) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)
Ceded Credit Risk [Line Items]
Insured Financial Obligations, Net Par Exposures Reassumed	$ 118.0
Assured Guaranty Re [Member]
Ceded Credit Risk [Line Items]
Amounts could be required to pay if third party exercised right to recapture business		$ 41.0
AGC [Member]
Ceded Credit Risk [Line Items]
Amounts could be required to pay if third party exercised right to recapture business		248.0
Standard & Poor's, A Rating [Member] | Uncollateralized [Member]
Ceded Credit Risk [Line Items]
Guaranty Liabilities	1.3	1.3
AM Best, A- Rating [Member] | Uncollateralized [Member]
Ceded Credit Risk [Line Items]
Guaranty Liabilities	$ 13.0	$ 13.0