Fair Value - Level 3 Unobservable Inputs, Mortgage Servicing Rights - Initial Recognition (Details)	3 Months Ended		12 Months Ended
	Mar. 31, 2022 USD ($) item	Mar. 31, 2021 USD ($) item	Dec. 31, 2021 USD ($) item
Mortgage servicing rights
Inputs
Amount recognized | $	$ 616,302,000	$ 470,533,000
Total | Mortgage servicing rights | Level 3 | Minimum
Inputs:
Annual per-loan cost of servicing | $	79		$ 79
Total | Mortgage servicing rights | Level 3 | Maximum
Inputs:
Annual per-loan cost of servicing | $	175		197
Total | Mortgage servicing rights | Level 3 | Weighted average
Inputs:
Annual per-loan cost of servicing | $	$ 107		$ 108
Total | Mortgage servicing rights | Pricing spread | Level 3 | Minimum
Inputs:
Input	4.9		5.3
Total | Mortgage servicing rights | Pricing spread | Level 3 | Maximum
Inputs:
Input	15.2		15.5
Total | Mortgage servicing rights | Pricing spread | Level 3 | Weighted average
Inputs:
Input	7.3		7.7
Total | Mortgage servicing rights | Annual total prepayment speed | Level 3 | Minimum
Inputs:
Input	6.4		7.9
Total | Mortgage servicing rights | Annual total prepayment speed | Level 3 | Maximum
Inputs:
Input	24.4		26.7
Total | Mortgage servicing rights | Annual total prepayment speed | Level 3 | Weighted average
Inputs:
Input	8.9		10.7
Total | Mortgage servicing rights | Life | Level 3 | Minimum
Inputs:
Input	3.4		3.1
Total | Mortgage servicing rights | Life | Level 3 | Maximum
Inputs:
Input	8.7		7.7
Total | Mortgage servicing rights | Life | Level 3 | Weighted average
Inputs:
Input	7.6		6.8
Total | MSRs at the time of initial recognition, excluding MSR purchases | Level 3
Inputs
Amount recognized | $	$ 616,302,000	470,533,000
Unpaid principal balance of underlying loans | $	$ 30,575,969,000	$ 34,943,254,000
Weighted-average servicing fee rate (as a percent)	0.43%	0.34%
Total | MSRs at the time of initial recognition, excluding MSR purchases | Level 3 | Minimum
Inputs:
Annual per-loan cost of servicing | $	$ 80	$ 81
Total | MSRs at the time of initial recognition, excluding MSR purchases | Level 3 | Maximum
Inputs:
Annual per-loan cost of servicing | $	177	117
Total | MSRs at the time of initial recognition, excluding MSR purchases | Level 3 | Weighted average
Inputs:
Annual per-loan cost of servicing | $	$ 104	$ 104
Total | MSRs at the time of initial recognition, excluding MSR purchases | Pricing spread | Level 3 | Minimum
Inputs:
Input	5.8	8.0
Total | MSRs at the time of initial recognition, excluding MSR purchases | Pricing spread | Level 3 | Maximum
Inputs:
Input	16.1	16.9
Total | MSRs at the time of initial recognition, excluding MSR purchases | Pricing spread | Level 3 | Weighted average
Inputs:
Input	7.5	9.6
Total | MSRs at the time of initial recognition, excluding MSR purchases | Annual total prepayment speed | Level 3 | Minimum
Inputs:
Input	6.0	6.2
Total | MSRs at the time of initial recognition, excluding MSR purchases | Annual total prepayment speed | Level 3 | Maximum
Inputs:
Input	23.4	12.9
Total | MSRs at the time of initial recognition, excluding MSR purchases | Annual total prepayment speed | Level 3 | Weighted average
Inputs:
Input	8.3	7.8
Total | MSRs at the time of initial recognition, excluding MSR purchases | Life | Level 3 | Minimum
Inputs:
Input	3.7	4.1
Total | MSRs at the time of initial recognition, excluding MSR purchases | Life | Level 3 | Maximum
Inputs:
Input	8.8	9.0
Total | MSRs at the time of initial recognition, excluding MSR purchases | Life | Level 3 | Weighted average
Inputs:
Input	8.3	8.5