Junior Surplus Notes issued by the Segregated Account of Ambac Assurance to Ambac upon Ambac's emergence from bankruptcy. These Junior Surplus notes will be includable in surplus for statutory accounting purposes as prescribed or permitted by state laws and regulations.

No definition available.

Long-Term Debt (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		12 Months Ended
Long-Term Debt (Details) - USD ($) $ in Thousands	Jul. 31, 2015	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Feb. 12, 2018	Dec. 31, 2016	May 01, 2013	May 19, 2011
Debt Instrument [Line Items]
Tier 2 Note Security in RMBS Litigation Settlement Proceeds					$ 1,600,000
Secured Debt		$ 65,196		$ 73,993
One Time Interest Payment on Surplus Notes					13,501
Junior surplus note of Ambac Assurance Segregated Account							$ 350,000
5.1% Junior Surplus Notes, General Account Due 2020 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage		19.50%
Debt Instrument, Face Amount		$ 369,315		370,237
Ambac Note Post Exit From Rehabilitation [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage		7.60%
Debt Instrument, Face Amount		$ 2,154,351
Tier 2 Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		8.50%
Tier 2 Note Security in RMBS Litigation Settlement Proceeds		$ 1,600,000
Debt Instrument, Interest Rate, Effective Percentage		9.90%
Paid-in-Kind Interest		$ 2,777
Debt Instrument, Face Amount		242,777
Secured Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount		$ 65,196		73,993
5.1% Surplus Notes, General Account, Due 2020 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage		10.50%
Debt Instrument Principal Amount Subject To Repurchase					463,624
Debt Instrument, Face Amount		$ 291,187		754,811
One State Street [Member] \| 5.1% Junior Surplus Notes, General Account Due 2020 [Member]
Debt Instrument [Line Items]
Debt Instrument Principal Amount Subject To Repurchase								$ 13,056
Debt Instrument, Face Amount		19,315		20,237
Extinguishment of Debt, Amount		$ 922	$ 977
Variable Interest Entity, Not Primary Beneficiary, Aggregated Disclosure [Member] \| 5.1% Junior Surplus Notes, Segregated Account Due 2020 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage		8.40%
Successor [Member]
Debt Instrument [Line Items]
Long-term debt		$ 2,957,732		991,696
Net realized gains (losses) on extinguishment of debt		3,115	$ 2,741
Successor [Member] \| Ambac Assurance Corporation [Member]
Debt Instrument [Line Items]
Long-term debt		2,957,732		991,696
Secured Debt		65,196		73,993
Successor [Member] \| Ambac Assurance Corporation [Member] \| 5.1% Junior Surplus Notes, General Account Due 2020 [Member]
Debt Instrument [Line Items]
Long-term debt		249,226		249,036
Successor [Member] \| Ambac Assurance Corporation [Member] \| Ambac Note Post Exit From Rehabilitation [Member]
Debt Instrument [Line Items]
Long-term debt		2,148,369		0
Successor [Member] \| Ambac Assurance Corporation [Member] \| Tier 2 Notes [Member]
Debt Instrument [Line Items]
Long-term debt		233,948		0
Successor [Member] \| Ambac Assurance Corporation [Member] \| 5.1% Surplus Notes, General Account, Due 2020 [Member]
Debt Instrument [Line Items]
Long-term debt		$ 260,993		668,667
Successor [Member] \| Variable Interest Entity [Member]
Debt Instrument [Line Items]
Long-term debt				$ 12,160,544
Successor [Member] \| 5.1% Junior Surplus Notes, General Account Due 2020 [Member] \| Ambac Assurance Corporation [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage				5.10%
Debt Instruments Maturity Year				2020
Successor [Member] \| 5.1% Surplus Notes, General Account, Due 2020 [Member] \| Ambac Assurance Corporation [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		5.10%		5.10%
Debt Instruments Maturity Year		2020		2020
Consolidated Variable Interest Entities [Member]
Debt Instrument [Line Items]
Unpaid Principal Amount Of Fixed Rate Debt Accounted For Under Fair Value Option		$ 9,679,441				$ 9,387,884
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months		295,651
Long-term Debt, Maturities, Repayments of Principal in Year Two		44,100
Long-term Debt, Maturities, Repayments of Principal in Year Three		94,024
Long-term Debt, Maturities, Repayments of Principal in Year Four		0
Long-term Debt, Maturities, Repayments of Principal in Year Five		$ 0
Consolidated Variable Interest Entities [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage		1.04%		0.96%
Consolidated Variable Interest Entities [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage		8.35%		8.35%
London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Interest Rate on Ambac Note Post Exit From Rehabilitation		5.00%
Interest Rate on Securities Issued by Delaware Trust	2.80%
London Interbank Offered Rate (LIBOR) [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Interest Rate on Ambac Note Post Exit From Rehabilitation		1.00%
Ambac [Member]
Debt Instrument [Line Items]
One Time Interest Payment on Surplus Notes					$ 2,618