Mortgage Servicing Rights - Summary of Adverse Changes to Weighted-Average Assumptions on the Fair Value of Servicing Rights (Details) - Mortgage servicing rights - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2024	Dec. 31, 2023
Actual
Option adjusted spread (percent)	5.20%	5.40%
Constant prepayment rate (as a percent)	7.90%	7.90%
Weighted average cost to service per loan	$ 68	$ 69
10% adverse change
Option adjusted spread	(20)	(20)
Constant prepayment rate	(40)	(37)
Weighted average cost to service per loan	(11)	(10)
20% adverse change
Option adjusted spread	(39)	(39)
Constant prepayment rate	(77)	(71)
Weighted average cost to service per loan	$ (22)	$ (21)