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v3.23.1

Regulatory Capital Requirements (Narrative) (Details) | 12 Months Ended
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Dec. 31, 2022
Regulatory Capital Requirements [Abstract] |
Percentage of Capital Stock and Surplus on Secured Basis | 10.00%

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- Definition Percentage of Capital Stock and Surplus on Secured Basis. + References No definition available. + Details
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Namespace Prefix: | func_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

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- References No definition available. + Details
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Namespace Prefix: | us-gaap_
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Balance Type: | na
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