Estimated Fair Values Estimated Fair Values (Fair Value Option) (Details) (Loans Held For Sale, USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Dec. 31, 2014
Loans Held For Sale
Fair Value, Option, Quantitative Disclosures [Line Items]
Gains (Losses) From Fair Value Changes	$ 430
Fair Value Of Items For Which Fair Value Option Was Elected Assets	66,508	63,696
Aggregate Unpaid Principal Balance Of Items For Which Fair Value Option Was Elected Assets	65,378	62,996
Fair Value Option Aggregate Difference Assets	$ 1,130	$ 700

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

No definition available.

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Namespace Prefix:	fcnca_
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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Period Type:	duration

- Details

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