Income Taxes Income Taxes - NOL Usage Table (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
	Mar. 31, 2016	Sep. 30, 2011	Dec. 31, 2015
Net Income Loss Reconciliation [Line Items]
Income Tax Examination, Penalties and Interest Accrued		$ 3,650,000
Percentage Of Notional Federal Tax Liability		25.00%
Tolling Payment Payable to AFG	$ 70,911
TierABCCredit	10,000
TierACreditUsage	5,000
NOL allocated amount	4,325,337
Ambac Assurance [Member]
Net Income Loss Reconciliation [Line Items]
AACNetTaxableIncome	(83,530)		$ 877,313
NOL allocated amount	2,772,677
AACNetTaxableIncomeFromTierA			479,000
AACNetTaxableIncomeFromTierB			398,313
AFG [Member]
Net Income Loss Reconciliation [Line Items]
NOL allocated amount	1,383,898
Tier B [Member]
Net Income Loss Reconciliation [Line Items]
NOL allocated amount			$ 1,057,000
PrePostDetermination [Domain] | Ambac Assurance [Member]
Net Income Loss Reconciliation [Line Items]
NOL allocated amount	$ 2,856,207