Mortgage Servicing Rights - Summary of Income and Fees (Details) - Residential first mortgage - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Servicing Assets at Fair Value
Decrease in MSR fair value due to pay-offs, pay-downs, run-off, model changes, and other			$ (31)
Changes in fair value			9
Net (loss) return on mortgage servicing rights
Servicing Assets at Fair Value
Servicing fees, ancillary income and late fees	$ 96	$ 65	60
Decrease in MSR fair value due to pay-offs, pay-downs, run-off, model changes, and other	(89)	(20)	(31)
Changes in fair value	(76)	2	9
Gain (loss) on MSR derivatives	76	(5)	(8)
Net transaction costs	(1)	(6)	(8)
Total return (loss) included in net return on mortgage servicing rights	6	36	22
Loan Administration Income
Servicing Assets at Fair Value
Servicing fees, ancillary income and late fees	106	54	35
Charges on subserviced custodial balances	(67)	(29)	(11)
Other servicing charges	(9)	(2)	(3)
Total income on mortgage loans subserviced, included in loan administration	$ 30	$ 23	$ 21