Income Taxes Income Taxes - Provision for Income Taxes Charged To Income From Continuing Operations (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Apr. 01, 2023
Provision for Income Taxes [Line Items]
Current Federal Tax Expense (Benefit)	$ 0	$ 0	$ 0	$ 0
Income (Loss) from Continuing Operations before Income Taxes, Domestic	(27)	(50)	(10)	(306)
Current Income Tax Expense (Benefit)	2	3	7	1
Deferred Foreign Income Tax Expense (Benefit)	9	(1)	6	(6)
Deferred Income Tax Expense (Benefit)	9	(1)	6	(6)
Income Tax Expense (Benefit)	11	2	13	(4)
Income (Loss) from Continuing Operations before Income Taxes, Foreign	10	17	12	(13)
Pre-tax income (loss)	(18)	(33)	1	(320)
Current State and Local Tax Expense (Benefit)	0	0	2	0
Current Foreign Tax Expense (Benefit)	$ 2	$ 3	5	$ 1
Ambac UK [Member]
Provision for Income Taxes [Line Items]
Deferred Income Taxes and Tax Credits			$ 6
Statutory Effective Income Tax Rate	19.00%		19.00%
Ambac UK [Member] | Subsequent Event
Provision for Income Taxes [Line Items]
Statutory Effective Income Tax Rate					25.00%