Fair Value - Level 3 Unobservable Inputs, Mortgage Servicing Rights, Effect of Change In Inputs on Fair Value (Details)	9 Months Ended	12 Months Ended
	Sep. 30, 2025 USD ($) Y	Dec. 31, 2024 USD ($) Y
MSR and pool characteristics
Carrying value	$ 9,653,942,000	$ 8,744,528,000
Mortgage servicing liabilities | Level 3
Prepayment speed
Annual per-loan cost of servicing	837	969
Total | Mortgage servicing rights | Level 3
MSR and pool characteristics
Carrying value	9,653,942,000	8,744,528,000
Unpaid principal balance of underlying loans	$ 470,281,735,000	$ 426,055,220,000
Weighted-average note interest rate (as a percent)	4.90%	4.50%
Weighted-average servicing fee rate (as a percent)	0.39%	0.38%
Pricing spread
Effect on fair value of 5% adverse change	$ (100,106,000)	$ (113,419,000)
Effect on fair value of 10% adverse change	(197,972,000)	(223,960,000)
Effect on fair value of 20% adverse change	(387,269,000)	(436,805,000)
Prepayment speed
Effect on fair value of 5% adverse change	(165,204,000)	(126,224,000)
Effect on fair value of 10% adverse change	(324,196,000)	(248,349,000)
Effect on fair value of 20% adverse change	(624,901,000)	(481,100,000)
Annual per-loan cost of servicing
Effect on fair value of 5% adverse change	(51,908,000)	(48,830,000)
Effect on fair value of 10% adverse change	(103,817,000)	(97,661,000)
Effect on fair value of 20% adverse change	(207,633,000)	(195,321,000)
Total | Mortgage servicing rights | Level 3 | Minimum
Prepayment speed
Annual per-loan cost of servicing	70	68
Total | Mortgage servicing rights | Level 3 | Maximum
Prepayment speed
Annual per-loan cost of servicing	127	130
Total | Mortgage servicing rights | Level 3 | Weighted average
Prepayment speed
Annual per-loan cost of servicing	$ 106	$ 105
Total | Mortgage servicing rights | Annual total prepayment speed | Level 3 | Minimum
Inputs
Input	0.06	0.059
Total | Mortgage servicing rights | Annual total prepayment speed | Level 3 | Maximum
Inputs
Input	0.227	0.177
Total | Mortgage servicing rights | Annual total prepayment speed | Level 3 | Weighted average
Inputs
Input	0.089	0.078
Total | Mortgage servicing rights | Life | Level 3 | Minimum
Inputs
Input | Y	2.5	2.7
Total | Mortgage servicing rights | Life | Level 3 | Maximum
Inputs
Input | Y	9	9.1
Total | Mortgage servicing rights | Life | Level 3 | Weighted average
Inputs
Input | Y	8	8.4
Total | Mortgage servicing rights | Option-adjusted spread | Level 3 | Minimum
Inputs
Input	0.021
Total | Mortgage servicing rights | Option-adjusted spread | Level 3 | Maximum
Inputs
Input	0.132
Total | Mortgage servicing rights | Option-adjusted spread | Level 3 | Weighted average
Inputs
Input	0.049
Total | Mortgage servicing rights | Pricing spread | Level 3 | Minimum
Inputs
Input		0.05
Total | Mortgage servicing rights | Pricing spread | Level 3 | Maximum
Inputs
Input		0.113
Total | Mortgage servicing rights | Pricing spread | Level 3 | Weighted average
Inputs
Input		0.062