Mortgage Servicing Rights - Summary of Income and Fees (Details) - Residential first mortgage loans - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Servicing Assets at Fair Value [Line Items]
Decreases in MSR fair value due to pay-offs, pay-downs, run-off, model changes, and other	$ (14)	$ (25)	$ (85)	$ (74)
Changes in fair value due to interest rate risk	7	2	58	(57)
Net return (loss) on mortgage servicing rights
Servicing Assets at Fair Value [Line Items]
Servicing fees, ancillary income and late fees	27	30	87	75
Decreases in MSR fair value due to pay-offs, pay-downs, run-off, model changes, and other	(14)	(25)	(85)	(74)
Changes in fair value due to interest rate risk	7	2	58	(57)
Gain (loss) on MSR derivatives	(5)	4	(43)	68
Net transaction costs	(6)	1	(13)	(2)
Total return included in net return on mortgage servicing rights	9	12	4	10
Loan administration income on mortgage loans subserviced
Servicing Assets at Fair Value [Line Items]
Servicing fees, ancillary income and late fees	36	33	101	94
Charges on subserviced custodial balances	(3)	(3)	(8)	(26)
Other servicing charges	(3)	(4)	(8)	(9)
Total income on mortgage loans subserviced, included in loan administration	$ 30	$ 26	$ 85	$ 59