Fair Value Measurements, Fair Value Of Financial Instruments as Measured On a Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2020		Dec. 31, 2019		Mar. 31, 2019	Dec. 31, 2018
Assets: [Abstract]
Trading securities	$ 2,110,585		$ 1,623,921
Available for sale securities	12,694,277		11,269,643
Fair value option securities	1,703,238		1,098,577
Mortgage servicing rights	110,828		201,886		$ 238,193	$ 259,254
Derviative contracts, net of cash collateral, Assets, Fair value	922,716		323,375
Liabilities: [Abstract]
Derivative contracts, net of cash collateral, Liabilities, Fair Value	1,213,445		251,128
U.S. government agency debentures [Member]
Assets: [Abstract]
Trading securities	37,740		44,264
Residential agency mortgage-backed securities [Member]
Assets: [Abstract]
Trading securities	1,922,725		1,504,651
Available for sale securities	9,259,089		8,046,096
Fair value option securities	1,703,238		1,088,660
Municipal and other tax-exempt securities [Member]
Assets: [Abstract]
Trading securities	35,513		26,196
Available for sale securities	24,034		1,861
Asset-backed securities [Member]
Assets: [Abstract]
Trading securities	58,278		14,084
U.S. Treasury [Member]
Assets: [Abstract]
Available for sale securities	917		1,600
Fair value option securities	0		9,917
Residential non-agency mortgage-backed securities [Member]
Assets: [Abstract]
Available for sale securities	34,866		41,609
Commercial agency mortgage-backed securities [Member]
Assets: [Abstract]
Available for sale securities	3,374,899		3,178,005
Other debt securities [Member]
Assets: [Abstract]
Trading securities	56,329		34,726
Available for sale securities	472		472
Fair Value, Recurring [Member]
Assets: [Abstract]
Trading securities	2,110,585		1,623,921
Available for sale securities	12,694,277		11,269,643
Fair value option securities	1,703,238		1,098,577
Residential mortgage loans held for sale	204,720		182,271
Mortgage servicing rights	110,828	[1]	201,886	[2]
Derviative contracts, net of cash collateral, Assets, Fair value	922,716	[3]	323,375	[4]
Liabilities: [Abstract]
Derivative contracts, net of cash collateral, Liabilities, Fair Value	1,213,445	[3]	251,128	[4]
Fair Value, Recurring [Member] | U.S. government agency debentures [Member]
Assets: [Abstract]
Trading securities	37,740		44,264
Fair Value, Recurring [Member] | Residential agency mortgage-backed securities [Member]
Assets: [Abstract]
Trading securities	1,922,725		1,504,651
Available for sale securities	9,259,089		8,046,096
Fair value option securities	1,703,238		1,088,660
Fair Value, Recurring [Member] | Municipal and other tax-exempt securities [Member]
Assets: [Abstract]
Trading securities	35,513		26,196
Available for sale securities	24,034		1,861
Fair Value, Recurring [Member] | Asset-backed securities [Member]
Assets: [Abstract]
Trading securities	58,278		14,084
Fair Value, Recurring [Member] | U.S. Treasury [Member]
Assets: [Abstract]
Available for sale securities	917		1,600
Fair value option securities	0		9,917
Fair Value, Recurring [Member] | Residential non-agency mortgage-backed securities [Member]
Assets: [Abstract]
Available for sale securities	34,866		41,609
Fair Value, Recurring [Member] | Commercial agency mortgage-backed securities [Member]
Assets: [Abstract]
Available for sale securities	3,374,899		3,178,005
Fair Value, Recurring [Member] | Other debt securities [Member]
Assets: [Abstract]
Trading securities	56,329		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	917		1,600
Fair value option securities	0		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	83,268	[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	917		1,600
Fair value option securities	0		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	2,110,585		1,623,921
Available for sale securities	12,692,888		11,267,571
Fair value option securities	1,703,238		1,088,660
Residential mortgage loans held for sale	195,146		173,958
Mortgage servicing rights	0	[1]	0	[2]
Derviative contracts, net of cash collateral, Assets, Fair value	839,448	[3]	314,431	[4]
Liabilities: [Abstract]
Derivative contracts, net of cash collateral, Liabilities, Fair Value	1,213,445	[3]	251,128	[4]
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | U.S. government agency debentures [Member]
Assets: [Abstract]
Trading securities	37,740		44,264
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Residential agency mortgage-backed securities [Member]
Assets: [Abstract]
Trading securities	1,922,725		1,504,651
Available for sale securities	9,259,089		8,046,096
Fair value option securities	1,703,238		1,088,660
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Municipal and other tax-exempt securities [Member]
Assets: [Abstract]
Trading securities	35,513		26,196
Available for sale securities	24,034		1,861
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Asset-backed securities [Member]
Assets: [Abstract]
Trading securities	58,278		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	34,866		41,609
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Commercial agency mortgage-backed securities [Member]
Assets: [Abstract]
Available for sale securities	3,374,899		3,178,005
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Other debt securities [Member]
Assets: [Abstract]
Trading securities	56,329		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	9,574		8,313
Mortgage servicing rights	110,828	[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, interest rate and agricultural 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 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.