Fair Value Measurements, Fair Value Of Financial Instruments as Measured On a Recurring Basis (Details) - USD ($) $ in Thousands	Jun. 30, 2019		Mar. 31, 2019	Dec. 31, 2018		Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Assets: [Abstract]
Trading securities	$ 1,900,395			$ 1,956,923
Available for sale securities	10,514,414			8,857,120
Fair value option securities	1,138,819			283,235
Mortgage servicing rights	208,308		$ 238,193	259,254		$ 278,719	$ 274,978	$ 252,867
Derviative contracts, net of cash collateral, Assets, Fair value	415,221			320,929
Liabilities: [Abstract]
Derivative contracts, net of cash collateral, Liabilities, Fair Value	381,454			362,306
U.S. government agency debentures [Member]
Assets: [Abstract]
Trading securities	83,148			63,765
Residential agency mortgage-backed securities [Member]
Assets: [Abstract]
Trading securities	1,620,613			1,791,584
Available for sale securities	7,354,741			5,804,708
Municipal and other tax-exempt securities [Member]
Assets: [Abstract]
Trading securities	49,718			34,507
Available for sale securities	2,470			2,864
Asset-backed securities [Member]
Assets: [Abstract]
Trading securities	93,546			42,656
U.S. Treasury [Member]
Assets: [Abstract]
Available for sale securities	1,889			493
Residential non-agency mortgage-backed securities [Member]
Assets: [Abstract]
Available for sale securities	47,057			59,736
Commercial mortgage-backed securities guaranteed by U.S. government agencies [Member]
Assets: [Abstract]
Available for sale securities	3,107,785			2,953,889
Other debt securities [Member]
Assets: [Abstract]
Trading securities	53,370			24,411
Available for sale securities	472			35,430
Fair Value, Recurring [Member]
Assets: [Abstract]
Trading securities	1,900,395			1,956,923
Available for sale securities	10,514,414			8,857,120
Residential mortgage loans held for sale	193,570			149,221
Mortgage servicing rights	208,308	[1]		259,254	[2]
Derviative contracts, net of cash collateral, Assets, Fair value	415,221	[3]		320,929	[4]
Liabilities: [Abstract]
Derivative contracts, net of cash collateral, Liabilities, Fair Value	381,454	[3]		362,306	[4]
Fair Value, Recurring [Member] | U.S. government agency debentures [Member]
Assets: [Abstract]
Trading securities	83,148			63,765
Fair Value, Recurring [Member] | Residential agency mortgage-backed securities [Member]
Assets: [Abstract]
Trading securities	1,620,613			1,791,584
Available for sale securities	7,354,741			5,804,708
Fair value option securities	1,138,820			283,235
Fair Value, Recurring [Member] | Municipal and other tax-exempt securities [Member]
Assets: [Abstract]
Trading securities	49,718			34,507
Available for sale securities	2,470			2,864
Fair Value, Recurring [Member] | Asset-backed securities [Member]
Assets: [Abstract]
Trading securities	93,546			42,656
Fair Value, Recurring [Member] | U.S. Treasury [Member]
Assets: [Abstract]
Available for sale securities	1,889			493
Fair Value, Recurring [Member] | Residential non-agency mortgage-backed securities [Member]
Assets: [Abstract]
Available for sale securities	47,057			59,736
Fair Value, Recurring [Member] | Commercial mortgage-backed securities guaranteed by U.S. government agencies [Member]
Assets: [Abstract]
Available for sale securities	3,107,785			2,953,889
Fair Value, Recurring [Member] | Other debt securities [Member]
Assets: [Abstract]
Trading securities	53,370			24,411
Available for sale securities	472			35,430
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Assets: [Abstract]
Trading securities	0			0
Available for sale securities	1,889			493
Residential mortgage loans held for sale	0			0
Mortgage servicing rights	0	[1]		0	[2]
Derviative contracts, net of cash collateral, Assets, Fair value	29,352	[3]		44,074	[4]
Liabilities: [Abstract]
Derivative contracts, net of cash collateral, Liabilities, Fair Value	0	[3]		0	[4]
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | U.S. government agency debentures [Member]
Assets: [Abstract]
Trading securities	0			0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Residential agency mortgage-backed securities [Member]
Assets: [Abstract]
Trading securities	0			0
Available for sale securities	0			0
Fair value option securities	0			0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Municipal and other tax-exempt securities [Member]
Assets: [Abstract]
Trading securities	0			0
Available for sale securities	0			0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Asset-backed securities [Member]
Assets: [Abstract]
Trading securities	0			0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | U.S. Treasury [Member]
Assets: [Abstract]
Available for sale securities	1,889			493
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Residential non-agency mortgage-backed securities [Member]
Assets: [Abstract]
Available for sale securities	0			0
Fair Value, 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
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Other debt securities [Member]
Assets: [Abstract]
Trading securities	0			0
Available for sale securities	0			0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Assets: [Abstract]
Trading securities	1,900,395			1,956,923
Available for sale securities	10,512,053			8,856,155
Residential mortgage loans held for sale	177,497			134,014
Mortgage servicing rights	0	[1]		0	[2]
Derviative contracts, net of cash collateral, Assets, Fair value	385,869	[3]		276,855	[4]
Liabilities: [Abstract]
Derivative contracts, net of cash collateral, Liabilities, Fair Value	381,454	[3]		362,306	[4]
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | U.S. government agency debentures [Member]
Assets: [Abstract]
Trading securities	83,148			63,765
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Residential agency mortgage-backed securities [Member]
Assets: [Abstract]
Trading securities	1,620,613			1,791,584
Available for sale securities	7,354,741			5,804,708
Fair value option securities	1,138,820			283,235
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Municipal and other tax-exempt securities [Member]
Assets: [Abstract]
Trading securities	49,718			34,507
Available for sale securities	2,470			2,864
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Asset-backed securities [Member]
Assets: [Abstract]
Trading securities	93,546			42,656
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | U.S. Treasury [Member]
Assets: [Abstract]
Available for sale securities	0			0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Residential non-agency mortgage-backed securities [Member]
Assets: [Abstract]
Available for sale securities	47,057			59,736
Fair Value, 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	3,107,785			2,953,889
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Other debt securities [Member]
Assets: [Abstract]
Trading securities	53,370			24,411
Available for sale securities	0			34,958
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Assets: [Abstract]
Trading securities	0			0
Available for sale securities	472			472
Residential mortgage loans held for sale	16,073			15,207
Mortgage servicing rights	208,308	[1]		259,254	[2]
Derviative contracts, net of cash collateral, Assets, Fair value	0	[3]		0	[4]
Liabilities: [Abstract]
Derivative contracts, net of cash collateral, Liabilities, Fair Value	0	[3]		0	[4]
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | U.S. government agency debentures [Member]
Assets: [Abstract]
Trading securities	0			0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Residential agency mortgage-backed securities [Member]
Assets: [Abstract]
Trading securities	0			0
Available for sale securities	0			0
Fair value option securities	0			0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Municipal and other tax-exempt securities [Member]
Assets: [Abstract]
Trading securities	0			0
Available for sale securities				0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Asset-backed securities [Member]
Assets: [Abstract]
Trading securities	0			0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | U.S. Treasury [Member]
Assets: [Abstract]
Available for sale securities	0			0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Residential non-agency mortgage-backed securities [Member]
Assets: [Abstract]
Available for sale securities	0			0
Fair Value, 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
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Other debt securities [Member]
Assets: [Abstract]
Trading securities	0			0
Available for sale securities	$ 472			$ 472

[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] 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, net of cash margin. 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, fully offset by 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 interest rate, 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 contracts, fully offset by cash margin.