Consolidated Balance Sheets - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Assets:
Estimated Fair Value	$ 2,949	$ 3,314
Other Investments	595	478
Investments, Total	3,544	3,792
Cash and cash equivalents	20	24
Restricted Cash	13	55
Premiums Receivable, Net	370	416
Deferred ceded premium	70	82
Subrogation recoverable	2,156	2,029
Derivative assets	93	75
Income Taxes Receivable, Current	0	11
Intangible assets	409	427
Other assets	114	95
Total assets	13,220	13,320
Liabilities:
Unearned premiums	456	518
Loss and loss expense reserves	1,759	1,548
Ceded premiums payable	27	29
Deferred Income Tax Liabilities, Net	24	32
Taxes Payable, Current	6	0
Long-term debt	2,739	2,822
Accrued interest payable	517	441
Derivative liabilities	114	90
Other liabilities	106	93
Variable interest entity liabilities:
Total liabilities	$ 12,074	$ 11,783
Preferred Stock, Shares Outstanding	0	0
Preferred stock, shares authorized	20,000,000	20,000,000
Stockholders’ equity:
Preferred Stock, Value, Issued	$ 0	$ 0
Common Stock, Value, Issued	0	0
Additional paid-in capital	242	232
Accumulated other comprehensive income (loss)	79	42
Retained earnings	759	1,203
Treasury Stock, Value	(1)	0
Total Ambac Financial Group, Inc. stockholders’ equity	1,080	1,477
Nonredeemable noncontrolling interest	60	60
Total stockholders’ equity	1,140	1,536
Total liabilities, redeemable noncontrolling interest and stockholders’ equity	13,220	13,320
Debt Securities, Available-for-sale, Allowance for Credit Loss	0
Uncollectable premium receivables	17
Reinsurance Recoverables, Including Reinsurance Premium Paid	33	$ 26
Reinsurance Recoverable, Allowance for Credit Loss	$ 0
Preferred stock, par value	$ 0.01	$ 0.01
Common stock, shares issued	45,865,081	45,571,743
Common stock, shares authorized	130,000,000	130,000,000
Common Stock, Par or Stated Value Per Share	$ 0.01	$ 0.01
Fixed income securities, amortized cost	$ 2,807	$ 3,187
Xchange
Stockholders’ equity:
Redeemable Noncontrolling Interest, Equity, Carrying Amount	7
Variable Interest Entity [Member]
Assets:
Estimated Fair Value	3,354	3,121
Restricted Cash	2	2
Loans, at fair value	2,998	3,108
Derivative assets	41	52
Other assets	2	3
Total assets	6,398	6,286
Variable interest entity assets:
Loans, at fair value	2,998	3,108
Liabilities:
Long-term debt	4,493	4,554
Accrued interest payable	0	1
Derivative liabilities	1,835	1,657
Variable interest entity liabilities:
Total liabilities	6,328	6,212
Stockholders’ equity:
Long-term Debt	4,324	4,351
Fixed Income Securities [Member]
Assets:
Estimated Fair Value	2,317	2,577
Investment income due and accrued	10
Stockholders’ equity:
Debt Securities, Available-for-sale, Allowance for Credit Loss	0
Fixed income securities, amortized cost	2,175	2,450
Short-term Investments [Member]
Assets:
Estimated Fair Value	492	653
Collateral Pledged [Member]
Assets:
Estimated Fair Value	140
Collateral Pledged [Member] | Fixed Income Securities [Member]
Assets:
Estimated Fair Value	15	85
Stockholders’ equity:
Fixed income securities, amortized cost	15	0
Collateral Pledged [Member] | Short-term Investments [Member]
Assets:
Estimated Fair Value	125	85
Stockholders’ equity:
Fixed income securities, amortized cost	$ 125	$ 85