Fair Value Measurements, Fair Value Of Financial Instruments as Measured On a Recurring Basis (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014		Mar. 31, 2014		Dec. 31, 2013
Assets: [Abstract]
Trading securities	$ 118,044		$ 188,700		$ 86,571
Available for sale securities	9,158,175		8,978,945		9,933,723
Fair value option securities	434,077		311,597		160,884
Mortgage servicing rights	175,051		171,976		153,774		153,333
Derviative contracts, net of cash margin, Assets, Fair value	462,386		361,874		218,507
Liabilities: [Abstract]
Derivative contracts, net of cash margin, Liabilities, Fair Value	419,351		354,554		185,499
U.S. Government agency debentures [Member]
Assets: [Abstract]
Trading securities	26,283		85,092		28,588
U.S. agency residential mortgage-backed securities [Member]
Assets: [Abstract]
Trading securities	17,179		31,199		23,595
Available for sale securities	6,717,569		6,646,884		7,475,569
Fair value option securities	434,077		311,597		156,525
Municipal and other tax-exempt securities [Member]
Assets: [Abstract]
Trading securities	54,164		38,951		27,280
Available for sale securities	60,818		63,557		70,065
Other trading securities [Member]
Assets: [Abstract]
Trading securities	20,418		33,458		7,108
U.S. Treasury [Member]
Assets: [Abstract]
Available for sale securities	1,001		1,005		1,034
Privately issued residential mortgage-backed securities [Member]
Assets: [Abstract]
Available for sale securities	160,031		165,957		189,248
Commercial mortgage-backed securities guaranteed by U.S. government agencies [Member]
Assets: [Abstract]
Available for sale securities	2,164,842		2,048,609		2,123,762
Other debt securities [Member]
Assets: [Abstract]
Available for sale securities	9,155		9,212		35,119
Fair value option securities	0		0		4,359
Perpetual preferred stock [Member]
Assets: [Abstract]
Available for sale securities	24,983		24,277		24,281
Equity securities and mutual funds [Member]
Assets: [Abstract]
Available for sale securities	19,776		19,444		14,645
Fair Value, Measurements, Recurring [Member]
Assets: [Abstract]
Trading securities	118,044		188,700		86,571
Available for sale securities	9,158,175		8,978,945		9,933,723
Fair value option securities	434,077		311,597		160,884
Residential mortgage loans held for sale	513,196		304,182		226,512
Mortgage servicing rights	175,051	[1]	171,976	[1]	153,774	[1]
Derviative contracts, net of cash margin, Assets, Fair value	462,386	[2]	361,874	[3]	218,507	[4]
Other assets, private equity funds	25,565		25,627		27,466
Liabilities: [Abstract]
Derivative contracts, net of cash margin, Liabilities, Fair Value	419,351	[2]	354,554	[3]	185,499	[4]
Fair Value, Measurements, Recurring [Member] | U.S. Government agency debentures [Member]
Assets: [Abstract]
Trading securities	26,283		85,092		28,588
Fair Value, Measurements, Recurring [Member] | U.S. agency residential mortgage-backed securities [Member]
Assets: [Abstract]
Trading securities	17,179		31,199		23,595
Available for sale securities	6,717,569		6,646,884		7,475,569
Fair value option securities	434,077		311,597		156,525
Fair Value, Measurements, Recurring [Member] | Municipal and other tax-exempt securities [Member]
Assets: [Abstract]
Trading securities	54,164		38,951		27,280
Available for sale securities	60,818		63,557		70,065
Fair Value, Measurements, Recurring [Member] | Other trading securities [Member]
Assets: [Abstract]
Trading securities	20,418		33,458		7,108
Fair Value, Measurements, Recurring [Member] | U.S. Treasury [Member]
Assets: [Abstract]
Available for sale securities	1,001		1,005		1,034
Fair Value, Measurements, Recurring [Member] | Privately issued residential mortgage-backed securities [Member]
Assets: [Abstract]
Available for sale securities	160,031		165,957		189,248
Fair Value, Measurements, Recurring [Member] | Commercial mortgage-backed securities guaranteed by U.S. government agencies [Member]
Assets: [Abstract]
Available for sale securities	2,164,842		2,048,609		2,123,762
Fair Value, Measurements, Recurring [Member] | Other debt securities [Member]
Assets: [Abstract]
Available for sale securities	9,155		9,212		35,119
Fair value option securities	0		0		4,359
Fair Value, Measurements, Recurring [Member] | Perpetual preferred stock [Member]
Assets: [Abstract]
Available for sale securities	24,983		24,277		24,281
Fair Value, Measurements, Recurring [Member] | Equity securities and mutual funds [Member]
Assets: [Abstract]
Available for sale securities	19,776		19,444		14,645
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Assets: [Abstract]
Trading securities	0		0		0
Available for sale securities	6,072		5,932		1,034
Fair value option securities	0		0		0
Residential mortgage loans held for sale	0		0		0
Mortgage servicing rights	0	[1]	0	[1]	0	[1]
Derviative contracts, net of cash margin, Assets, Fair value	21,369	[2]	17,607	[3]	1,363	[4]
Other assets, private equity funds	0		0		0
Liabilities: [Abstract]
Derivative contracts, net of cash margin, Liabilities, Fair Value	0	[2]	541	[3]	0	[4]
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | U.S. Government agency debentures [Member]
Assets: [Abstract]
Trading securities	0		0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | U.S. agency residential mortgage-backed securities [Member]
Assets: [Abstract]
Trading securities	0		0		0
Available for sale securities	0		0		0
Fair value option securities	0		0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Municipal and other tax-exempt securities [Member]
Assets: [Abstract]
Trading securities	0		0		0
Available for sale securities	0		0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Other trading securities [Member]
Assets: [Abstract]
Trading securities	0		0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | U.S. Treasury [Member]
Assets: [Abstract]
Available for sale securities	1,001		1,005		1,034
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Privately issued residential mortgage-backed securities [Member]
Assets: [Abstract]
Available for sale securities	0		0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Commercial mortgage-backed securities guaranteed by U.S. government agencies [Member]
Assets: [Abstract]
Available for sale securities	0		0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Other debt securities [Member]
Assets: [Abstract]
Available for sale securities	0		0		0
Fair value option securities	0		0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Perpetual preferred stock [Member]
Assets: [Abstract]
Available for sale securities	0		0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Equity securities and mutual funds [Member]
Assets: [Abstract]
Available for sale securities	5,071		4,927		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Assets: [Abstract]
Trading securities	118,044		188,700		86,571
Available for sale securities	9,138,330		8,958,770		9,912,454
Fair value option securities	434,077		311,597		160,884
Residential mortgage loans held for sale	506,326		292,326		226,512
Mortgage servicing rights	0	[1]	0	[1]	0	[1]
Derviative contracts, net of cash margin, Assets, Fair value	441,017	[2]	344,267	[3]	217,144	[4]
Other assets, private equity funds	0		0		0
Liabilities: [Abstract]
Derivative contracts, net of cash margin, Liabilities, Fair Value	419,351	[2]	354,013	[3]	185,499	[4]
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | U.S. Government agency debentures [Member]
Assets: [Abstract]
Trading securities	26,283		85,092		28,588
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | U.S. agency residential mortgage-backed securities [Member]
Assets: [Abstract]
Trading securities	17,179		31,199		23,595
Available for sale securities	6,717,569		6,646,884		7,475,569
Fair value option securities	434,077		311,597		156,525
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Municipal and other tax-exempt securities [Member]
Assets: [Abstract]
Trading securities	54,164		38,951		27,280
Available for sale securities	51,195		53,464		54,542
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Other trading securities [Member]
Assets: [Abstract]
Trading securities	20,418		33,458		7,108
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | U.S. Treasury [Member]
Assets: [Abstract]
Available for sale securities	0		0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Privately issued residential mortgage-backed securities [Member]
Assets: [Abstract]
Available for sale securities	160,031		165,957		189,248
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Commercial mortgage-backed securities guaranteed by U.S. government agencies [Member]
Assets: [Abstract]
Available for sale securities	2,164,842		2,048,609		2,123,762
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Other debt securities [Member]
Assets: [Abstract]
Available for sale securities	5,005		5,062		30,407
Fair value option securities	0		0		4,359
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Perpetual preferred stock [Member]
Assets: [Abstract]
Available for sale securities	24,983		24,277		24,281
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Equity securities and mutual funds [Member]
Assets: [Abstract]
Available for sale securities	14,705		14,517		14,645
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Assets: [Abstract]
Trading securities	0		0		0
Available for sale securities	13,773		14,243		20,235
Fair value option securities	0		0		0
Residential mortgage loans held for sale	6,870		11,856		0
Mortgage servicing rights	175,051	[1]	171,976	[1]	153,774	[1]
Derviative contracts, net of cash margin, Assets, Fair value	0	[2]	0	[3]	0	[4]
Other assets, private equity funds	25,565		25,627		27,466
Liabilities: [Abstract]
Derivative contracts, net of cash margin, Liabilities, Fair Value	0	[2]	0	[3]	0	[4]
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | U.S. Government agency debentures [Member]
Assets: [Abstract]
Trading securities	0		0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | U.S. agency residential mortgage-backed securities [Member]
Assets: [Abstract]
Trading securities	0		0		0
Available for sale securities	0		0		0
Fair value option securities	0		0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Municipal and other tax-exempt securities [Member]
Assets: [Abstract]
Trading securities	0		0		0
Available for sale securities	9,623		10,093		15,523
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Other trading securities [Member]
Assets: [Abstract]
Trading securities	0		0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | U.S. Treasury [Member]
Assets: [Abstract]
Available for sale securities	0		0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Privately issued residential mortgage-backed securities [Member]
Assets: [Abstract]
Available for sale securities	0		0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Commercial mortgage-backed securities guaranteed by U.S. government agencies [Member]
Assets: [Abstract]
Available for sale securities	0		0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Other debt securities [Member]
Assets: [Abstract]
Available for sale securities	4,150		4,150		4,712
Fair value option securities	0		0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Perpetual preferred stock [Member]
Assets: [Abstract]
Available for sale securities	0		0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Equity securities and mutual funds [Member]
Assets: [Abstract]
Available for sale securities	$ 0		$ 0		$ 0

[1] A reconciliation of the beginning and ending fair value of mortgage servicing rights and disclosures of significant assumptions used to determine fair value are presented in Note 5, Mortgage Banking Activities.

[2] See Note 3 for detail of fair value of derivative contracts by contract type. Derivative contracts in asset positions that were valued based on quoted prices in active markets for identical instruments (Level 1) are primarily exchange-traded energy derivative contacts, net of cash margin. Derivative contacts in liability positions that were valued using quoted prices in active markets for identical instruments are exchange-traded agricultural derivative contracts, fully offset by cash margin.

[3] See Note 3 for detail of fair value of derivative contracts by contract type. Derivative contracts based on quoted prices in active markets for identical instruments (Level 1) are exchange-traded energy derivative contacts, net of cash margin. Derivative contracts in liability positions that were valued using quoted prices in active markets fro identical instruments (Level 1) are exchange-traded interest rate and agricultural derivative contracts, net of cash margin.

[4] See Note 3 for detail of fair value of derivative contracts by contract type. Derivative contracts based on quoted prices in active markets for identical instruments (Level 1) are exchange-traded energy and interest rate derivative contacts, net of cash margin.