Loans and Allowances for Credit Losses Part 1 (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
Loan receivables disclosure [Abstract]
Loans receivables with fixed rate of interest	$ 5,395,296,000	$ 4,934,153,000
Loans receivables with variable rate of interest	5,673,161,000	5,478,069,000
Loan receivable non-accrual	201,286,000	230,814,000
Total	11,269,743,000	10,643,036,000
Accruing loans past due (90 days)	2,498,000	7,966,000
Foregone interest on nonaccrual loans	11,726,000	16,818,000
Loans receivable, other information [Abstract]
Amount of total loan portfolio to businesses and individuals in Oklahoma	5,000,000,000	4,900,000,000
Percentage of total loan portfolio to businesses and individuals in Oklahoma (in hundredths)	44.00%	46.00%
Amount of total loan portfolio to businesses and individuals in Texas	3,400,000,000	3,000,000,000
Percentage of total loan portfolio to businesses and individuals in Texas (in hundredths)	31.00%	28.00%
Balance of loans with balances less than $10 million	11,269,743,000	10,643,036,000
Credit Commitments [Abstract]
Outstanding commitments to extend credit	6,100,000,000
Outstanding standby letters of credit	37,000,000
Outstanding commercial letters of credit	7,400,000
Percentage of committed production loans secured by properties primarily producing oil	51.00%
Percentage of committed production loans secured by properties primarily producing gas	47.00%
Commercial Portfolio Segment [Member]
Loan receivables disclosure [Abstract]
Loans receivables with fixed rate of interest	3,272,862,000	2,883,905,000
Loans receivables with variable rate of interest	3,229,781,000	3,011,636,000
Loan receivable non-accrual	68,811,000	38,455,000
Total	6,571,454,000	5,933,996,000
Loans receivable, other information [Abstract]
Balance of loans with balances less than $10 million	6,571,454,000	5,933,996,000
Amount of loan portfolio to businesses in Oklahoma	2,700,000,000	2,600,000,000
Percentage of loan portfolio to businesses in Oklahoma (in hundredths)	41.00%	43.00%
Amount of loan portfolio to businesses in Texas	2,200,000,000	1,900,000,000
Percentage of loan portfolio to businesses in Texas (in hundredths)	34.00%	32.00%
Commercial Portfolio Segment [Member] | Commercial Energy Financing Receivable [Member]
Loan receivables disclosure [Abstract]
Total	993,000,000,000
Loans receivable, other information [Abstract]
Percentage of total loan portfolio provided to this classification (in hundredths)	18.00%
Balance of loans with balances less than $10 million	993,000,000,000
Maximum loan amount for certain individual loans in category	10,000,000
Commercial Portfolio Segment [Member] | Commercial Services Financing Receivable [Member]
Loan receivables disclosure [Abstract]
Total		1,000,000,000
Loans receivable, other information [Abstract]
Balance of loans with balances less than $10 million		1,000,000,000
Maximum loan amount for certain individual loans in category		10,000,000
Commercial Real Estate Portfolio Segment [Member]
Loan receivables disclosure [Abstract]
Loans receivables with fixed rate of interest	887,923,000	829,836,000
Loans receivables with variable rate of interest	1,293,793,000	1,297,148,000
Loan receivable non-accrual	99,193,000	150,366,000
Total	2,279,909,000	2,277,350,000
Loans receivable, other information [Abstract]
Balance of loans with balances less than $10 million	2,279,909,000	2,277,350,000
Percentage of loan portfolio secured by property in Texas (in hundredths)	36.00%	30.00%
Percentage of loan portfolio secured by property in Oklahoma (in hundredths)	26.00%	32.00%
Residential Portfolio Segment [Member]
Loan receivables disclosure [Abstract]
Loans receivables with fixed rate of interest	992,556,000	851,048,000
Loans receivables with variable rate of interest	948,138,000	939,774,000
Loan receivable non-accrual	29,767,000	37,426,000
Total	1,970,461,000	1,828,248,000
Loans receivable, other information [Abstract]
Balance of loans with balances less than $10 million	1,970,461,000	1,828,248,000
Minimum FICO required for jumbo loan approval	720
Maximum debt-to-income ratio on jumbo loans (in hundredths)	38.00%
Minimum loan-to-value ratio on jumbo loans (in hundredths)	60.00%
Maximum loan-to-value ratio on jumbo loans (in hundredths)	100.00%
Minimum period for fixed rate on variable rate jumbo loans (in years)	3Y
Maximum period for fixed rate on variable rate jumbo loans (in years)	10Y
Amount of loans guaranteed by US government and previously sold into GNMA mortgage pools	185,000,000	72,000,000
Consumer Portfolio Segment [Member]
Loan receivables disclosure [Abstract]
Loans receivables with fixed rate of interest	241,955,000	369,364,000
Loans receivables with variable rate of interest	202,449,000	229,511,000
Loan receivable non-accrual	3,515,000	4,567,000
Total	447,919,000	603,442,000
Loans receivable, other information [Abstract]
Balance of loans with balances less than $10 million	$ 447,919,000	$ 603,442,000