Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Successor [Member]
Assets:
Fixed income securities, at fair value (amortized cost of $4,514,878 in 2014 and $5,927,254 in 2013)	$ 4,725,686	$ 5,885,316
Fixed income securities pledged as collateral, at fair value (amortized cost of $64,378 in 2014 and $126,196 in 2013)	64,267	126,223
Short-term investments, at fair value (amortized cost of $360,069 in 2014 and $271,118 in 2013)	360,065	271,119
Other investments (includes $336,013 at fair value in 2014 and $271,118 in 2013)	357,016	241,069
Total investments	5,507,034	6,523,727
Cash and cash equivalents	73,903	77,370
Receivable for securities	23,660	14,450
Investment income due and accrued	25,015	37,663
Premium receivables	1,000,607	1,453,021
Reinsurance recoverable on paid and unpaid losses	99,838	121,249
Deferred ceded premium	123,276	145,529
Subrogation recoverable	953,274	498,478
Loans	5,714	6,179
Derivative assets	109,017	77,711
Insurance intangible asset	1,410,920	1,597,965
Goodwill	514,511	514,511
Other assets	186,985	35,927
Total assets	25,159,864	27,092,477
Liabilities:
Unearned premiums	1,673,785	2,255,680
Loss and loss expense reserves	4,752,007	5,968,712
Ceded premiums payable	60,436	70,962
Obligations under investment agreements	160,079	359,070
Deferred taxes	2,079	2,199
Current taxes	5,701	738
Long-term debt	971,116	963,178
Accrued interest payable	304,139	294,817
Derivative liabilities	406,944	253,898
Other liabilities	63,396	67,377
Payable for securities purchased	762	4,654
Total liabilities	23,486,129	26,114,055
Stockholders’ equity:
Preferred stock, par value $0.01 per share; authorized shares—20,000,000; issued and outstanding shares—none	0	0
Common stock, par value $0.01 per share; authorized shares—130,000,000; issued and outstanding shares—45,005,932 at December 31, 2014 and 45,003,461 at December 31, 2013	450	450
Additional paid-in capital	189,138	185,672
Accumulated other comprehensive income	220,283	11,661
Accumulated earnings	989,290	505,219
Common stock held in treasury at cost, 2,459 shares at December 31, 2014 and 937 shares at December 31, 2013	(56)	(19)
Total Ambac Financial Group, Inc. stockholders’ equity	1,399,105	702,983
Noncontrolling interest	274,630	275,439
Total stockholders’ equity	1,673,735	978,422
Total liabilities and stockholders’ equity	25,159,864	27,092,477
Successor [Member] | Variable Interest Entity [Member]
Variable interest entity assets:
Fixed income securities, at fair value	2,743,050	2,475,182
Restricted cash	7,708	17,498
Investment income due and accrued	1,284	1,365
Loans, at fair value	12,371,177	13,398,895
Intangible assets	0	76,140
Other assets	2,891	19,617
Variable interest entity liabilities:
Accrued interest payable	3,268	722
Long-term debt, at fair value	12,882,076	14,091,753
Derivative liabilities	2,200,163	1,772,306
Other liabilities	$ 178	$ 7,989