Insurance Regulatory Restrictions Additional Details (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Average Annual Rate Of Return	5.43%	5.87%
Prescribed Discount Rate Percentage	5.10%
Statutory Accounting Practices, Statutory Capital and Surplus Required	$ 100
REDUCTION TO GROSS PAID-IN AND CONNTRIBUTED SURPLUS	$ 3,433
Statutory Accounting Practices, Statutory Capital and Surplus Required Pursuant to AMPS Exchange		$ 75
Quarterly Dividend Increase Limitation Percentage	15.00%
Percentage Of Policy Holders Surplus	10.00%
Minimum [Member]
Settlement Agreement Annual Restricted Payment Amount	$ 5
Maximum [Member]
Settlement Agreement Annual Restricted Payment Amount	8
Ambac Assurance [Member]
Statutory Accounting Practices, Statutory Capital and Surplus, Balance	1,088	1,152
Ambac Assurance [Member] | Prescribed Or Permitted Additional Accounting Practices [Member]
Statutory Accounting Practices, Prescribed Practice, Amount	$ (12)	$ (42)
5.1 % Surplus Notes Due 2020 [Member] | Ambac Assurance Corporation [Member]
Debt Instrument, Interest Rate, Stated Percentage		5.10%	5.10%