Derivative Financial Instruments - Narrative (Detail) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Derivative [Line Items]
Credit exposure to settled variation margin in excess of customer related interest rate swap	$ 0.0	$ 0.1
Non Cleared Derivative Transactions \| Customer Related Interest Rate Swap Derivatives
Derivative [Line Items]
Fair value of interest rate swap liabilities that are net in a net liability position	28.3	42.6
Non Cleared Derivative Transactions \| Cash and cash equivalents \| Customer Related Interest Rate Swap Derivatives
Derivative [Line Items]
Additional collateral posted	35.9
Non Cleared Derivative Transactions \| Available-for-sale Securities \| Customer Related Interest Rate Swap Derivatives
Derivative [Line Items]
Additional collateral posted		49.2
Restricted Assets
Derivative [Line Items]
Initial margin collateral posted cash	49.3
Initial margin collateral posted treasury note		$ 60.4
Interest Income \| Termination Of Cash Flow Hedges
Derivative [Line Items]
Interest rate swap cash flow hedges amount expected to reclassified from other comprehensive income to income statement in the next twelve months	$ 28.3

Credit exposure to settled variation margin in excess of customer related interest rate swap.

No definition available.

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- Definition

The aggregate fair value of additional assets that would be required to be posted as collateral for derivative instruments with credit-risk-related contingent features if the credit-risk-related contingent features were triggered at the end of the reporting period.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4H
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- Definition

Fair value of credit risk derivative asset after deduction of credit risk derivative liability.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4K
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- Definition

Amount of right to receive cash collateral under master netting arrangements that have not been offset against derivative liabilities.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
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- Definition

Amount of right to receive securities collateral under master netting arrangements that have not been offset against derivative liabilities.

+ References

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

The estimated net amount of unrealized gains or losses on interest rate cash flow hedges as of the balance sheet date expected to be reclassified to earnings within the next twelve months.

+ References

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-Publisher FASB
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