Estimated Fair Values Estimated Fair Values (Fair Value Option) (Details) - Loans Held For Sale - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2015	Dec. 31, 2014
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value, Option, Changes in Fair Value, Gain (Loss)	$ 176	$ 202
Fair Value Of Items For Which Fair Value Option Was Elected Assets	59,766	63,696
Aggregate Unpaid Principal Balance Of Items For Which Fair Value Option Was Elected Assets	58,890	62,996
Fair Value Option Aggregate Difference Assets	$ 876	$ 700

Represents the aggregate unpaid principal balance of assets for which the fair value option was elected.

No definition available.

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Data Type:	xbrli:monetaryItemType
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Period Type:	instant

- Definition

Represents the fair value of assets for which the fair value option was elected.

+ References

No definition available.

+ Details

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Namespace Prefix:	fcnca_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

For assets for which the fair value option has been elected, this item represents the difference between the fair value and the aggregate unpaid principal balance for those assets.

+ References

No definition available.

+ Details

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Namespace Prefix:	fcnca_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

For each line item in the statement of financial position, the amounts of gains and losses from fair value changes included in earnings.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 30
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6957238&loc=d3e14172-108612

+ Details

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Balance Type:	credit
Period Type:	duration

- 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.

+ Details

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- Details

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