Fair Value Measurements, Fair Value Of Financial Instruments as Measured On a Recurring Basis (Details) - USD ($) $ in Thousands	Jun. 30, 2017		Mar. 31, 2017	Dec. 31, 2016		Jun. 30, 2016		Mar. 31, 2016	Dec. 31, 2015
Assets: [Abstract]
Trading securities	$ 441,414			$ 337,628		$ 211,622
Available for sale securities	8,341,041			8,676,829		8,830,689
Fair value option securities	445,169			77,046		263,265
Mortgage servicing rights	245,239		$ 249,403	247,073		190,747		$ 196,055	$ 218,605
Derviative contracts, net of cash collateral, Assets, Fair value	280,289			689,872		883,673
Liabilities: [Abstract]
Derivative contracts, net of cash collateral, Liabilities, Fair Value	285,819			664,531		719,159
U.S. government agency debentures
Assets: [Abstract]
Trading securities	20,954			6,234		18,909
U.S. government agency residential mortgage-backed securities
Assets: [Abstract]
Trading securities	365,171			310,067		122,306
Available for sale securities	5,382,377			5,460,386		5,700,268
Fair value option securities	445,169			77,046		237,959
Municipal and other tax-exempt securities
Assets: [Abstract]
Trading securities	45,444			14,427		52,721
Available for sale securities	32,765			40,993		50,262
Other trading securities
Assets: [Abstract]
Trading securities	9,845			6,900		17,686
U.S. Treasury
Assets: [Abstract]
Available for sale securities	998			999		1,004
Fair value option securities	0			0		25,306
Privately issued residential mortgage-backed securities
Assets: [Abstract]
Available for sale securities	103,383			115,535		126,313
Commercial mortgage-backed securities guaranteed by U.S. government agencies
Assets: [Abstract]
Available for sale securities	2,782,070			3,017,933		2,911,946
Other debt securities
Assets: [Abstract]
Available for sale securities	4,152			4,152		4,151
Perpetual preferred stock
Assets: [Abstract]
Available for sale securities	16,568			18,474		17,931
Equity securities and mutual funds
Assets: [Abstract]
Available for sale securities	18,728			18,357		18,814
Fair Value, Measurements, Recurring [Member]
Assets: [Abstract]
Trading securities	441,414			337,628		211,622
Available for sale securities	8,341,041			8,676,829		8,830,689
Fair value option securities						263,265
Residential mortgage loans held for sale	287,259			301,897		430,728
Mortgage servicing rights	245,239	[1]		247,073	[2]	190,747	[3]
Derviative contracts, net of cash collateral, Assets, Fair value	280,289	[4]		689,872	[5]	883,673	[6]
Liabilities: [Abstract]
Derivative contracts, net of cash collateral, Liabilities, Fair Value	285,819	[4]		664,531	[5]	719,159	[6]
Fair Value, Measurements, Recurring [Member] | U.S. government agency debentures
Assets: [Abstract]
Trading securities	20,954			6,234		18,909
Fair Value, Measurements, Recurring [Member] | U.S. government agency residential mortgage-backed securities
Assets: [Abstract]
Trading securities	365,171			310,067		122,306
Available for sale securities	5,382,377			5,460,386		5,700,268
Fair value option securities	445,169			77,046		237,959
Fair Value, Measurements, Recurring [Member] | Municipal and other tax-exempt securities
Assets: [Abstract]
Trading securities	45,444			14,427		52,721
Available for sale securities	32,765			40,993		50,262
Fair Value, Measurements, Recurring [Member] | Other trading securities
Assets: [Abstract]
Trading securities	9,845			6,900		17,686
Fair Value, Measurements, Recurring [Member] | U.S. Treasury
Assets: [Abstract]
Available for sale securities	998			999		1,004
Fair value option securities						25,306
Fair Value, Measurements, Recurring [Member] | Privately issued residential mortgage-backed securities
Assets: [Abstract]
Available for sale securities	103,383			115,535		126,313
Fair Value, Measurements, Recurring [Member] | Commercial mortgage-backed securities guaranteed by U.S. government agencies
Assets: [Abstract]
Available for sale securities	2,782,070			3,017,933		2,911,946
Fair Value, Measurements, Recurring [Member] | Other debt securities
Assets: [Abstract]
Available for sale securities	4,152			4,152		4,151
Fair Value, Measurements, Recurring [Member] | Perpetual preferred stock
Assets: [Abstract]
Available for sale securities	16,568			18,474		17,931
Fair Value, Measurements, Recurring [Member] | Equity securities and mutual funds
Assets: [Abstract]
Available for sale securities	18,728			18,357		18,814
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Assets: [Abstract]
Trading securities	0			0		0
Available for sale securities	4,514			4,494		4,789
Fair value option securities						25,306
Residential mortgage loans held for sale	0			0		0
Mortgage servicing rights	0	[1]		0	[2]	0	[3]
Derviative contracts, net of cash collateral, Assets, Fair value	20,213	[4]		7,541	[5]	7,246	[6]
Liabilities: [Abstract]
Derivative contracts, net of cash collateral, Liabilities, Fair Value	5,919	[4]		6,972	[5]	4,808	[6]
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | U.S. government agency debentures
Assets: [Abstract]
Trading securities	0			0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | U.S. government agency residential mortgage-backed securities
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
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
Assets: [Abstract]
Trading securities	0			0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | U.S. Treasury
Assets: [Abstract]
Available for sale securities	998			999		1,004
Fair value option securities						25,306
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Privately issued residential mortgage-backed securities
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
Assets: [Abstract]
Available for sale securities	0			0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Other debt securities
Assets: [Abstract]
Available for sale securities	0			0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Perpetual preferred stock
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
Assets: [Abstract]
Available for sale securities	3,516			3,495		3,785
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Assets: [Abstract]
Trading securities	441,414			337,628		211,622
Available for sale securities	8,327,720			8,662,394		8,812,149
Fair value option securities						237,959
Residential mortgage loans held for sale	274,524			290,280		420,979
Mortgage servicing rights	0	[1]		0	[2]	0	[3]
Derviative contracts, net of cash collateral, Assets, Fair value	260,076	[4]		682,331	[5]	876,427	[6]
Liabilities: [Abstract]
Derivative contracts, net of cash collateral, Liabilities, Fair Value	279,900	[4]		657,559	[5]	714,351	[6]
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | U.S. government agency debentures
Assets: [Abstract]
Trading securities	20,954			6,234		18,909
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | U.S. government agency residential mortgage-backed securities
Assets: [Abstract]
Trading securities	365,171			310,067		122,306
Available for sale securities	5,382,377			5,460,386		5,700,268
Fair value option securities	445,169			77,046		237,959
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Municipal and other tax-exempt securities
Assets: [Abstract]
Trading securities	45,444			14,427		52,721
Available for sale securities	28,110			35,204		40,662
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Other trading securities
Assets: [Abstract]
Trading securities	9,845			6,900		17,686
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | U.S. Treasury
Assets: [Abstract]
Available for sale securities	0			0		0
Fair value option securities						0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Privately issued residential mortgage-backed securities
Assets: [Abstract]
Available for sale securities	103,383			115,535		126,313
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Commercial mortgage-backed securities guaranteed by U.S. government agencies
Assets: [Abstract]
Available for sale securities	2,782,070			3,017,933		2,911,946
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Other debt securities
Assets: [Abstract]
Available for sale securities	0			0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Perpetual preferred stock
Assets: [Abstract]
Available for sale securities	16,568			18,474		17,931
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Equity securities and mutual funds
Assets: [Abstract]
Available for sale securities	15,212			14,862		15,029
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Assets: [Abstract]
Trading securities	0			0		0
Available for sale securities	8,807			9,941		13,751
Fair value option securities						0
Residential mortgage loans held for sale	12,735			11,617		9,749
Mortgage servicing rights	245,239	[1]		247,073	[2]	190,747	[3]
Derviative contracts, net of cash collateral, Assets, Fair value	0	[4]		0	[5]	0	[6]
Liabilities: [Abstract]
Derivative contracts, net of cash collateral, Liabilities, Fair Value	0	[4]		0	[5]	0	[6]
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | U.S. government agency debentures
Assets: [Abstract]
Trading securities	0			0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | U.S. government agency residential mortgage-backed securities
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
Assets: [Abstract]
Trading securities	0			0		0
Available for sale securities	4,655			5,789		9,600
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Other trading securities
Assets: [Abstract]
Trading securities	0			0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | U.S. Treasury
Assets: [Abstract]
Available for sale securities	0			0		0
Fair value option securities						0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Privately issued residential mortgage-backed securities
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
Assets: [Abstract]
Available for sale securities	0			0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Other debt securities
Assets: [Abstract]
Available for sale securities	4,152			4,152		4,151
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Perpetual preferred stock
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
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 6, Mortgage Banking Activities.

[2] 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 6, Mortgage Banking Activities.

[3] 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 6, Mortgage Banking Activities.

[4] 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 and interest rate derivative contacts. Derivative contacts in liability positions that were valued using quoted prices in active markets for identical instruments are exchange-traded interest rate and agricultural derivative contracts, net of cash margin.

[5] 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 interest-rate and energy derivative contacts, net of cash margin. Derivative contracts in liability positions that were valued using quoted prices in active markets for identical instruments (Level 1) are exchange-traded interest rate, energy and agricultural derivative contracts, net of cash margin.

[6] 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 agricultural derivative contacts, net of cash margin. Derivative contracts in liability positions that were valued using quoted prices in active markets for identical instruments (Level 1) are exchange-traded interest rate and energy derivative contracts, net cash margin.