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Securities (Narrative) (Details) (USD $) In Billions	Sep. 30, 2011	Dec. 31, 2010
Securities [Abstract]
Carrying value of pledged securities	$ 2.2	$ 2.3

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- Definition

Carrying Value Of Pledged Securities

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

Securities

+ Details

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Namespace Prefix:	cfr
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration