Fair Value - Level 3 Unobservable Inputs, Mortgage Servicing Rights, Effect of Change In Inputs on Fair Value (Details)	3 Months Ended	12 Months Ended
	Mar. 31, 2024 USD ($) Y	Dec. 31, 2023 USD ($) Y
MSR and pool characteristics
Carrying value	$ 7,483,210,000	$ 7,099,348,000
Mortgage servicing liabilities | Level 3
Prepayment speed
Annual per-loan cost of servicing	992	1,043
Total | Mortgage servicing rights | Level 3
MSR and pool characteristics
Carrying value	7,483,210,000	7,099,348,000
Unpaid principal balance of underlying loans	$ 381,470,663,000	$ 370,244,119,000
Weighted-average note interest rate (as a percent)	4.20%	4.10%
Weighted-average servicing fee rate (as a percent)	0.38%	0.38%
Pricing spread
Effect on fair value of 5% adverse change	$ (98,475,000)	$ (94,307,000)
Effect on fair value of 10% adverse change	(194,382,000)	(186,129,000)
Effect on fair value of 20% adverse change	(378,857,000)	(362,671,000)
Prepayment speed
Effect on fair value of 5% adverse change	(110,071,000)	(107,757,000)
Effect on fair value of 10% adverse change	(216,317,000)	(211,643,000)
Effect on fair value of 20% adverse change	(418,132,000)	(408,638,000)
Annual per-loan cost of servicing
Effect on fair value of 5% adverse change	(45,114,000)	(44,572,000)
Effect on fair value of 10% adverse change	(90,228,000)	(89,145,000)
Effect on fair value of 20% adverse change	(180,457,000)	(178,289,000)
Total | Mortgage servicing rights | Level 3 | Minimum
Prepayment speed
Annual per-loan cost of servicing	70	70
Total | Mortgage servicing rights | Level 3 | Maximum
Prepayment speed
Annual per-loan cost of servicing	132	135
Total | Mortgage servicing rights | Level 3 | Weighted average
Prepayment speed
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