Fair Value Measurements, Fair Value Of Financial Instruments as Measured On a Recurring Basis (Details) - USD ($) $ in Thousands	Jun. 30, 2020		Mar. 31, 2020	Dec. 31, 2019		Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018
Assets: [Abstract]
Trading securities	$ 1,196,105			$ 1,623,921
Available for sale securities	12,475,919			11,269,643
Fair value option securities	722,657			1,098,577
Mortgage servicing rights	97,971		$ 110,828	201,886		$ 208,308	$ 238,193	$ 259,254
Derviative contracts, net of cash collateral, Assets, Fair value	651,553			323,375
Liabilities: [Abstract]
Derivative contracts, net of cash collateral, Liabilities, Fair Value	610,020			251,128
U.S. government agency debentures [Member]
Assets: [Abstract]
Trading securities	4,237			44,264
Residential agency mortgage-backed securities [Member]
Assets: [Abstract]
Trading securities	1,146,454			1,504,651
Available for sale securities	9,147,238			8,046,096
Fair value option securities	629,915			1,088,660
Municipal and other tax-exempt securities [Member]
Assets: [Abstract]
Trading securities	22,710			26,196
Available for sale securities	31,240			1,861
Asset-backed securities [Member]
Assets: [Abstract]
Trading securities	5			14,084
U.S. Treasury [Member]
Assets: [Abstract]
Available for sale securities	912			1,600
Fair value option securities	92,742			9,917
Residential non-agency mortgage-backed securities [Member]
Assets: [Abstract]
Available for sale securities	35,250			41,609
Commercial agency mortgage-backed securities [Member]
Assets: [Abstract]
Available for sale securities	3,260,807			3,178,005
Other debt securities [Member]
Assets: [Abstract]
Trading securities	22,699			34,726
Available for sale securities	472			472
Fair Value, Recurring [Member]
Assets: [Abstract]
Trading securities	1,196,105			1,623,921
Available for sale securities	12,475,919			11,269,643
Fair value option securities	722,657			1,098,577
Residential mortgage loans held for sale	319,357			182,271
Mortgage servicing rights	97,971	[1]		201,886	[2]
Derviative contracts, net of cash collateral, Assets, Fair value	651,553	[3]		323,375	[4]
Liabilities: [Abstract]
Derivative contracts, net of cash collateral, Liabilities, Fair Value	610,020	[3]		251,128	[4]
Fair Value, Recurring [Member] | U.S. government agency debentures [Member]
Assets: [Abstract]
Trading securities	4,237			44,264
Fair Value, Recurring [Member] | Residential agency mortgage-backed securities [Member]
Assets: [Abstract]
Trading securities	1,146,454			1,504,651
Available for sale securities	9,147,238			8,046,096
Fair value option securities	629,915			1,088,660
Fair Value, Recurring [Member] | Municipal and other tax-exempt securities [Member]
Assets: [Abstract]
Trading securities	22,710			26,196
Available for sale securities	31,240			1,861
Fair Value, Recurring [Member] | Asset-backed securities [Member]
Assets: [Abstract]
Trading securities	5			14,084
Fair Value, Recurring [Member] | U.S. Treasury [Member]
Assets: [Abstract]
Available for sale securities	912			1,600
Fair value option securities	92,742			9,917
Fair Value, Recurring [Member] | Residential non-agency mortgage-backed securities [Member]
Assets: [Abstract]
Available for sale securities	35,250			41,609
Fair Value, Recurring [Member] | Commercial agency mortgage-backed securities [Member]
Assets: [Abstract]
Available for sale securities	3,260,807			3,178,005
Fair Value, Recurring [Member] | Other debt securities [Member]
Assets: [Abstract]
Trading securities	22,699			34,726
Available for sale securities	472			472
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Assets: [Abstract]
Trading securities	0			0
Available for sale securities	912			1,600
Fair value option securities	92,742			9,917
Residential mortgage loans held for sale	0			0
Mortgage servicing rights	0	[1]		0	[2]
Derviative contracts, net of cash collateral, Assets, Fair value	66,207	[3]		8,944	[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	912			1,600
Fair value option securities	92,742			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	1,196,105			1,623,921
Available for sale securities	12,474,535			11,267,571
Fair value option securities	629,915			1,088,660
Residential mortgage loans held for sale	309,672			173,958
Mortgage servicing rights	0	[1]		0	[2]
Derviative contracts, net of cash collateral, Assets, Fair value	585,346	[3]		314,431	[4]
Liabilities: [Abstract]
Derivative contracts, net of cash collateral, Liabilities, Fair Value	610,020	[3]		251,128	[4]
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | U.S. government agency debentures [Member]
Assets: [Abstract]
Trading securities	4,237			44,264
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Residential agency mortgage-backed securities [Member]
Assets: [Abstract]
Trading securities	1,146,454			1,504,651
Available for sale securities	9,147,238			8,046,096
Fair value option securities	629,915			1,088,660
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Municipal and other tax-exempt securities [Member]
Assets: [Abstract]
Trading securities	22,710			26,196
Available for sale securities	31,240			1,861
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Asset-backed securities [Member]
Assets: [Abstract]
Trading securities	5			14,084
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			0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Residential non-agency mortgage-backed securities [Member]
Assets: [Abstract]
Available for sale securities	35,250			41,609
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Commercial agency mortgage-backed securities [Member]
Assets: [Abstract]
Available for sale securities	3,260,807			3,178,005
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Other debt securities [Member]
Assets: [Abstract]
Trading securities	22,699			34,726
Available for sale securities	0			0
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			0
Residential mortgage loans held for sale	9,685			8,313
Mortgage servicing rights	97,971	[1]		201,886	[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 option 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 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 5, 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 5, 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 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 and agricultural contracts, fully offset by cash margin.