Fair Value - Level 3 Unobservable Inputs, Mortgage Servicing Rights - Initial Recognition (Details)	3 Months Ended		12 Months Ended
	Mar. 31, 2024 USD ($) Y	Mar. 31, 2023 USD ($) Y	Dec. 31, 2023 USD ($) Y
Mortgage servicing rights
Inputs
Amount recognized	$ 412,520,000	$ 286,533,000
Total | Mortgage servicing rights | Level 3 | Minimum
Inputs:
Annual per-loan cost of servicing	70		$ 70
Total | Mortgage servicing rights | Level 3 | Maximum
Inputs:
Annual per-loan cost of servicing	132		135
Total | Mortgage servicing rights | Level 3 | Weighted average
Inputs:
Annual per-loan cost of servicing	$ 107		$ 107
Total | Mortgage servicing rights | Pricing spread | Level 3 | Minimum
Inputs:
Input	0.055		0.055
Total | Mortgage servicing rights | Pricing spread | Level 3 | Maximum
Inputs:
Input	0.126		0.126
Total | Mortgage servicing rights | Pricing spread | Level 3 | Weighted average
Inputs:
Input	0.064		0.064
Total | Mortgage servicing rights | Annual total prepayment speed | Level 3 | Minimum
Inputs:
Input	0.060		0.061
Total | Mortgage servicing rights | Annual total prepayment speed | Level 3 | Maximum
Inputs:
Input	0.176		0.178
Total | Mortgage servicing rights | Annual total prepayment speed | Level 3 | Weighted average
Inputs:
Input	0.079		0.083
Total | Mortgage servicing rights | Life | Level 3 | Minimum
Inputs:
Input | Y	3.0		3.0
Total | Mortgage servicing rights | Life | Level 3 | Maximum
Inputs:
Input | Y	9.0		9.0
Total | Mortgage servicing rights | Life | Level 3 | Weighted average
Inputs:
Input | Y	8.2		8.1
Total | Mortgage servicing rights | MSRs at the time of initial recognition, excluding MSR purchases | Level 3
Inputs
Amount recognized	$ 412,520,000	286,533,000
Unpaid principal balance of underlying loans	$ 19,484,815,000	$ 13,695,364,000
Weighted-average servicing fee rate (as a percent)	0.44%	0.50%
Total | Mortgage servicing rights | MSRs at the time of initial recognition, excluding MSR purchases | Level 3 | Minimum
Inputs:
Annual per-loan cost of servicing	$ 71	$ 68
Total | Mortgage servicing rights | MSRs at the time of initial recognition, excluding MSR purchases | Level 3 | Maximum
Inputs:
Annual per-loan cost of servicing	127	125
Total | Mortgage servicing rights | MSRs at the time of initial recognition, excluding MSR purchases | Level 3 | Weighted average
Inputs:
Annual per-loan cost of servicing	$ 99	$ 103
Total | Mortgage servicing rights | MSRs at the time of initial recognition, excluding MSR purchases | Pricing spread | Level 3 | Minimum
Inputs:
Input	0.055	0.055
Total | Mortgage servicing rights | MSRs at the time of initial recognition, excluding MSR purchases | Pricing spread | Level 3 | Maximum
Inputs:
Input	0.126	0.117
Total | Mortgage servicing rights | MSRs at the time of initial recognition, excluding MSR purchases | Pricing spread | Level 3 | Weighted average
Inputs:
Input	0.063	0.077
Total | Mortgage servicing rights | MSRs at the time of initial recognition, excluding MSR purchases | Annual total prepayment speed | Level 3 | Minimum
Inputs:
Input	0.079	0.092
Total | Mortgage servicing rights | MSRs at the time of initial recognition, excluding MSR purchases | Annual total prepayment speed | Level 3 | Maximum
Inputs:
Input	0.159	0.232
Total | Mortgage servicing rights | MSRs at the time of initial recognition, excluding MSR purchases | Annual total prepayment speed | Level 3 | Weighted average
Inputs:
Input	0.110	0.117
Total | Mortgage servicing rights | MSRs at the time of initial recognition, excluding MSR purchases | Life | Level 3 | Minimum
Inputs:
Input | Y	3.5	3.0
Total | Mortgage servicing rights | MSRs at the time of initial recognition, excluding MSR purchases | Life | Level 3 | Maximum
Inputs:
Input | Y	9.3	8.4
Total | Mortgage servicing rights | MSRs at the time of initial recognition, excluding MSR purchases | Life | Level 3 | Weighted average
Inputs:
Input | Y	7.5	7.3