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Derivative Instruments - Summary of Notional Amounts of AFS's Trading Derivative Products (Detail) - AFS [Member] - Successor [Member] - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Interest Rate Swap [Member]
Schedule Of Loans And Allowance For Loan By Class Individually And Collectively Evaluated For Impairment [Line Items]
Derivative products, Notional Amount	$ 372,586	$ 379,497
Interest Rate Swaps-Pay-Fixed/Receive-Variable [Member]
Schedule Of Loans And Allowance For Loan By Class Individually And Collectively Evaluated For Impairment [Line Items]
Derivative products, Notional Amount	1,462,639	1,428,264
Futures Contracts [Member]
Schedule Of Loans And Allowance For Loan By Class Individually And Collectively Evaluated For Impairment [Line Items]
Derivative products, Notional Amount	$ 1,740,000	$ 1,655,000

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- Definition

Schedule Of Loans And Allowance For Loan By Class Individually And Collectively Evaluated For Impairment [Line Items]

+ References

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- Definition

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

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