Fair Value Measurements, Fair Value Of Financial Instruments as Measured On a Recurring Basis (Details) - USD ($) $ in Thousands	Jun. 30, 2021		Mar. 31, 2021	Dec. 31, 2020		Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019
Assets: [Abstract]
Trading securities	$ 5,699,070			$ 4,707,975
Available for sale securities	13,317,922			13,050,665
Fair value option securities	60,432			114,982
Mortgage servicing rights	117,629		$ 132,915	101,172		$ 97,971	$ 110,828	$ 201,886
Derviative contracts, net of cash collateral, Assets, Fair value	1,701,443			810,688
Liabilities: [Abstract]
Derivative contracts, net of cash collateral, Liabilities, Fair Value	612,261			405,779
U.S. government securities [Member]
Assets: [Abstract]
Trading securities	13,481			9,183
Residential agency mortgage-backed securities [Member]
Assets: [Abstract]
Trading securities	5,577,986			4,669,148
Available for sale securities	8,624,876			9,340,471
Fair value option securities	60,432			114,982
Municipal securities [Member]
Assets: [Abstract]
Trading securities	49,636			19,172
Available for sale securities	386,509			167,979
U.S. Treasury [Member]
Assets: [Abstract]
Available for sale securities	504			508
Residential non-agency mortgage-backed securities [Member]
Assets: [Abstract]
Available for sale securities	28,261			32,770
Commercial agency mortgage-backed securities [Member]
Assets: [Abstract]
Available for sale securities	4,277,301			3,508,465
Other debt securities [Member]
Assets: [Abstract]
Trading securities	57,967			10,472
Available for sale securities	471			472
Fair Value, Recurring [Member]
Assets: [Abstract]
Trading securities	5,699,070			4,707,975
Available for sale securities	13,317,922			13,050,665
Fair value option securities				114,982
Residential mortgage loans held for sale	200,842	[1]		252,316	[2]
Mortgage servicing rights	117,629	[3]		101,172	[4]
Derviative contracts, net of cash collateral, Assets, Fair value	1,701,443	[5]		810,688	[6]
Liabilities: [Abstract]
Derivative contracts, net of cash collateral, Liabilities, Fair Value	612,261	[5]		405,779	[6]
Fair Value, Recurring [Member] | U.S. government securities [Member]
Assets: [Abstract]
Trading securities	13,481			9,183
Fair Value, Recurring [Member] | Residential agency mortgage-backed securities [Member]
Assets: [Abstract]
Trading securities	5,577,986			4,669,148
Available for sale securities	8,624,876			9,340,471
Fair value option securities	60,432
Fair Value, Recurring [Member] | Municipal securities [Member]
Assets: [Abstract]
Trading securities	49,636			19,172
Available for sale securities	386,509			167,979
Fair Value, Recurring [Member] | U.S. Treasury [Member]
Assets: [Abstract]
Available for sale securities	504			508
Fair Value, Recurring [Member] | Residential non-agency mortgage-backed securities [Member]
Assets: [Abstract]
Available for sale securities	28,261			32,770
Fair Value, Recurring [Member] | Commercial agency mortgage-backed securities [Member]
Assets: [Abstract]
Available for sale securities	4,277,301			3,508,465
Fair Value, Recurring [Member] | Other debt securities [Member]
Assets: [Abstract]
Trading securities				10,472
Available for sale securities	471			472
Fair Value, Recurring [Member] | Other trading securities
Assets: [Abstract]
Trading securities	57,967
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Assets: [Abstract]
Trading securities	4,999			4,999
Available for sale securities	504			508
Fair value option securities				0
Residential mortgage loans held for sale	0	[1]		0	[2]
Mortgage servicing rights	0	[3]		0	[4]
Derviative contracts, net of cash collateral, Assets, Fair value	7,704	[5]		10,780	[6]
Liabilities: [Abstract]
Derivative contracts, net of cash collateral, Liabilities, Fair Value	218	[5]		0	[6]
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | U.S. government securities [Member]
Assets: [Abstract]
Trading securities	4,999			4,999
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
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Municipal securities [Member]
Assets: [Abstract]
Trading securities	0			0
Available for sale securities	0			0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | U.S. Treasury [Member]
Assets: [Abstract]
Available for sale securities	504			508
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
Available for sale securities	0			0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Other trading securities
Assets: [Abstract]
Trading securities	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Assets: [Abstract]
Trading securities	5,694,071			4,702,976
Available for sale securities	13,316,947			13,049,685
Fair value option securities				114,982
Residential mortgage loans held for sale	195,692	[1]		245,299	[2]
Mortgage servicing rights	0	[3]		0	[4]
Derviative contracts, net of cash collateral, Assets, Fair value	1,693,739	[5]		799,908	[6]
Liabilities: [Abstract]
Derivative contracts, net of cash collateral, Liabilities, Fair Value	612,043	[5]		405,779	[6]
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | U.S. government securities [Member]
Assets: [Abstract]
Trading securities	8,482			4,184
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Residential agency mortgage-backed securities [Member]
Assets: [Abstract]
Trading securities	5,577,986			4,669,148
Available for sale securities	8,624,876			9,340,471
Fair value option securities	60,432
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Municipal securities [Member]
Assets: [Abstract]
Trading securities	49,636			19,172
Available for sale securities	386,509			167,979
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	28,261			32,770
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Commercial agency mortgage-backed securities [Member]
Assets: [Abstract]
Available for sale securities	4,277,301			3,508,465
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Other debt securities [Member]
Assets: [Abstract]
Trading securities				10,472
Available for sale securities	0			0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Other trading securities
Assets: [Abstract]
Trading securities	57,967
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Assets: [Abstract]
Trading securities	0			0
Available for sale securities	471			472
Fair value option securities				0
Residential mortgage loans held for sale	5,150	[1]		7,017	[2]
Mortgage servicing rights	117,629	[3]		101,172	[4]
Derviative contracts, net of cash collateral, Assets, Fair value	0	[5]		0	[6]
Liabilities: [Abstract]
Derivative contracts, net of cash collateral, Liabilities, Fair Value	$ 0	[5]		$ 0	[6]
Liquidity Discount on Mortgage Loans Qualifying for Sale to US Govt Agencies	95.57%			94.57%
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | U.S. government securities [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
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Municipal securities [Member]
Assets: [Abstract]
Trading securities	0			0
Available for sale securities				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 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
Available for sale securities	471			$ 472
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Other trading securities
Assets: [Abstract]
Trading securities	$ 0

[1] Residential mortgage loans held for sale measured at fair value on a recurring basis using significant unobservable inputs (Level 3) consist of residential mortgage loans intended for sale to U.S. government agencies that fail to meet conforming standards and are valued at 95.57% of the unpaid principal balance.

[2] Residential mortgage loans held for sale measured at fair value on a recurring basis using significant unobservable inputs (Level 3) consist of residential mortgage loans intended for sale to U.S. government agencies that fail to meet conforming standards and are valued at 94.57% of the unpaid principal balance.

[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 5, Mortgage Banking Activities.

[4] 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.

[5] See Note 3 for detail of fair value of derivative contracts by contract type. Fair values based on quoted prices in active markets for identical instruments (Level 1) are primarily exchange-traded derivative contracts, net of cash margin.

[6] See Note 3 for detail of fair value of derivative contracts by contract type. Fair values based on quoted prices in active markets for identical instruments (Level 1) are primarily exchange-traded derivative contracts, net of cash margin.