Fair Value Measurements, Fair Value Of Financial Instruments as Measured On a Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017	Dec. 31, 2016
Assets [Abstract]
Trading securities	$ 1,623,921		$ 1,956,923
Available for sale securities	11,269,643		8,857,120
Fair value option securities	1,098,577		283,235
Mortgage servicing rights	201,886		259,254		$ 252,867	$ 247,073
Derivative contracts, net of cash margin, Assets, Fair Value	323,375		320,929
Liabilities [Abstract]
Derivative contracts, net of cash margin, Liabilities, Fair Value	251,128		362,306
U.S. government agency debentures [Member]
Assets [Abstract]
Trading securities	44,264		63,765
Residential agency mortgage-backed securities [Member]
Assets [Abstract]
Trading securities	1,504,651		1,791,584
Available for sale securities	8,046,096		5,804,708
Fair value option securities	1,088,660		283,235
Municipal and other tax-exempt securities [Member]
Assets [Abstract]
Trading securities	26,196		34,507
Available for sale securities	1,861		2,864
Asset-backed securities [Member]
Assets [Abstract]
Trading securities	14,084		42,656
U.S. Treasury [Member]
Assets [Abstract]
Available for sale securities	1,600		493
Fair value option securities	9,917		0
Residential non-agency mortgage-backed securities [Member]
Assets [Abstract]
Available for sale securities	41,609		59,736
Commercial agency mortgage-backed securities [Member]
Assets [Abstract]
Available for sale securities	3,178,005		2,953,889
Other debt securities [Member]
Assets [Abstract]
Trading securities	34,726		24,411
Available for sale securities	472		35,430
Fair Value, Recurring [Member]
Assets [Abstract]
Trading securities	1,623,921		1,956,923
Available for sale securities	11,269,643		8,857,120
Fair value option securities	1,098,577
Residential mortgage loans held for sale	182,271		149,221
Mortgage servicing rights	201,886	[1]	259,254	[2]
Derivative contracts, net of cash margin, Assets, Fair Value	323,375	[3]	320,929	[4]
Liabilities [Abstract]
Derivative contracts, net of cash margin, Liabilities, Fair Value	251,128	[3]	362,306	[4]
Fair Value, Recurring [Member] | U.S. government agency debentures [Member]
Assets [Abstract]
Trading securities	44,264		63,765
Fair Value, Recurring [Member] | Residential agency mortgage-backed securities [Member]
Assets [Abstract]
Trading securities	1,504,651		1,791,584
Available for sale securities	8,046,096		5,804,708
Fair value option securities	1,088,660		283,235
Fair Value, Recurring [Member] | Municipal and other tax-exempt securities [Member]
Assets [Abstract]
Trading securities	26,196		34,507
Available for sale securities	1,861		2,864
Fair Value, Recurring [Member] | Asset-backed securities [Member]
Assets [Abstract]
Trading securities	14,084		42,656
Fair Value, Recurring [Member] | U.S. Treasury [Member]
Assets [Abstract]
Available for sale securities	1,600		493
Fair value option securities	9,917
Fair Value, Recurring [Member] | Residential non-agency mortgage-backed securities [Member]
Assets [Abstract]
Available for sale securities	41,609		59,736
Fair Value, Recurring [Member] | Commercial agency mortgage-backed securities [Member]
Assets [Abstract]
Available for sale securities	3,178,005		2,953,889
Fair Value, Recurring [Member] | Other debt securities [Member]
Assets [Abstract]
Trading securities	34,726		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	1,600		493
Fair value option securities	9,917
Residential mortgage loans held for sale	0		0
Mortgage servicing rights	0	[1]	0	[2]
Derivative contracts, net of cash margin, Assets, Fair Value	8,944	[3]	44,074	[4]
Liabilities [Abstract]
Derivative contracts, net of cash margin, 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	1,600		493
Fair value option securities	9,917
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 agency mortgage-backed securities [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	1,623,921		1,956,923
Available for sale securities	11,267,571		8,856,155
Fair value option securities	1,088,660
Residential mortgage loans held for sale	173,958		134,014
Mortgage servicing rights	0	[1]	0	[2]
Derivative contracts, net of cash margin, Assets, Fair Value	314,431	[3]	276,855	[4]
Liabilities [Abstract]
Derivative contracts, net of cash margin, Liabilities, Fair Value	251,128	[3]	362,306	[4]
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | U.S. government agency debentures [Member]
Assets [Abstract]
Trading securities	44,264		63,765
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Residential agency mortgage-backed securities [Member]
Assets [Abstract]
Trading securities	1,504,651		1,791,584
Available for sale securities	8,046,096		5,804,708
Fair value option securities	1,088,660		283,235
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Municipal and other tax-exempt securities [Member]
Assets [Abstract]
Trading securities	26,196		34,507
Available for sale securities	1,861		2,864
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Asset-backed securities [Member]
Assets [Abstract]
Trading securities	14,084		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 option securities	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Residential non-agency mortgage-backed securities [Member]
Assets [Abstract]
Available for sale securities	41,609		59,736
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Commercial agency mortgage-backed securities [Member]
Assets [Abstract]
Available for sale securities	3,178,005		2,953,889
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Other debt securities [Member]
Assets [Abstract]
Trading securities	34,726		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
Fair value option securities	0
Residential mortgage loans held for sale	8,313		15,207
Mortgage servicing rights	201,886	[1]	259,254	[2]
Derivative contracts, net of cash margin, Assets, Fair Value	0	[3]	0	[4]
Liabilities [Abstract]
Derivative contracts, net of cash margin, 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 option securities	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 agency mortgage-backed securities [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 7, 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 7, Mortgage Banking Activities.

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