Fair Value Measurements Fair Value Measurements (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011	Jun. 30, 2011
Fair Value Disclosures [Abstract]
Allowance for loan losses excluding loans held for sale	$ 191	$ 207	$ 259

The allowance for loan and lease losses, excluding loans held for sale, represents the reserve to cover probable credit losses related to specifically identified loans and leases, as well as probable credit losses inherent in the remainder of the loan portfolio as of the balance sheet date. For banks, include currently required allocated transfer risk reserves. Include carryover of or adjustments to the allowance for loan losses in connection with business combinations determined to be appropriate.

No definition available.

Name:	bokf_LoansAndLeasesReceivableExcludingLoansHeldForSaleAllowance
Namespace Prefix:	bokf_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant