Mortgage Servicing Rights - Summary of Income and Fees (Details) - Residential first mortgage - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Servicing Assets at Fair Value
Decrease in MSR fair value due to pay-offs, pay-downs, run-off, model changes and other	$ (109)	$ (89)	$ (20)
Changes in fair value due to interest rate risk	(50)	(76)	2
Net (loss) return on mortgage servicing rights
Servicing Assets at Fair Value
Servicing fees, ancillary income and late fees	107	96	65
Decrease in MSR fair value due to pay-offs, pay-downs, run-off, model changes and other	(109)	(89)	(20)
Changes in fair value due to interest rate risk	(50)	(76)	2
Gain (loss) on MSR derivatives	65	76	(5)
Net transaction costs	(3)	(1)	(6)
Total return (loss) included in net return on mortgage servicing rights	10	6	36
Loan administration income
Servicing Assets at Fair Value
Servicing fees, ancillary income and late fees	126	106	54
Charges on subserviced custodial balances	(29)	(67)	(29)
Other servicing charges	(13)	(9)	(2)
Total income on mortgage loans subserviced, included in loan administration	$ 84	$ 30	$ 23