Fair Value - Level 3 Unobservable Inputs, Mortgage Servicing Rights, Effect of Change In Inputs on Fair Value (Details)	12 Months Ended
	Dec. 31, 2021 USD ($) item	Dec. 31, 2020 USD ($) item
MSR and pool characteristics
Carrying value	$ 3,878,078,000	$ 2,581,174,000
Mortgage servicing liabilities | Level 3
Prepayment speed
Annual per-loan cost of servicing	1,406	305
Total | Mortgage servicing rights | Level 3
MSR and pool characteristics
Carrying value	3,878,078,000	2,581,174,000
Unpaid principal balance of underlying loans	$ 278,324,780,000	$ 238,410,809,000
Weighted-average note interest rate (as a percent)	3.20%	3.60%
Weighted-average servicing fee rate (as a percent)	0.34%	0.35%
Pricing spread
Effect on fair value of 5% adverse change	$ (59,577,000)	$ (46,356,000)
Effect on fair value of 10% adverse change	(117,352,000)	(90,936,000)
Effect on fair value of 20% adverse change	(227,791,000)	(175,137,000)
Prepayment speed
Effect on fair value of 5% adverse change	(80,109,000)	(66,536,000)
Effect on fair value of 10% adverse change	(157,252,000)	(130,253,000)
Effect on fair value of 20% adverse change	(303,259,000)	(249,843,000)
Annual per-loan cost of servicing
Effect on fair value of 5% adverse change	(32,979,000)	(25,482,000)
Effect on fair value of 10% adverse change	(65,958,000)	(50,964,000)
Effect on fair value of 20% adverse change	(131,916,000)	(101,929,000)
Total | Mortgage servicing rights | Level 3 | Minimum
Prepayment speed
Annual per-loan cost of servicing	79	79
Total | Mortgage servicing rights | Level 3 | Maximum
Prepayment speed
Annual per-loan cost of servicing	197	117
Total | Mortgage servicing rights | Level 3 | Weighted average
Prepayment speed
Annual per-loan cost of servicing	$ 108	$ 107
Total | Mortgage servicing rights | Pricing spread | Level 3 | Minimum
Inputs
Input | item	5.3	8.0
Total | Mortgage servicing rights | Pricing spread | Level 3 | Maximum
Inputs
Input | item	15.5	17.6
Total | Mortgage servicing rights | Pricing spread | Level 3 | Weighted average
Inputs
Input | item	7.7	10.1
Total | Mortgage servicing rights | Annual total prepayment speed | Level 3 | Minimum
Inputs
Input | item	7.9	10.1
Total | Mortgage servicing rights | Annual total prepayment speed | Level 3 | Maximum
Inputs
Input | item	26.7	32.9
Total | Mortgage servicing rights | Annual total prepayment speed | Level 3 | Weighted average
Inputs
Input | item	10.7	13.7
Total | Mortgage servicing rights | Life | Level 3 | Minimum
Inputs
Input | item	3.1	2.3
Total | Mortgage servicing rights | Life | Level 3 | Maximum
Inputs
Input | item	7.7	7.7
Total | Mortgage servicing rights | Life | Level 3 | Weighted average
Inputs
Input | item	6.8	6.0