Legal Proceedings, Contingencies and Commitments - Summary of the Contractual Amount of Significant Commitments (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Mortgage loan commitments including interest-rate locks
Loss Contingencies
Commitments to extend credit	$ 12,257	$ 4,099
Warehouse loan commitments
Loss Contingencies
Commitments to extend credit	2,218	1,944
Commercial and industrial commitments
Loss Contingencies
Commitments to extend credit	1,207	1,107
Other commercial commitments
Loss Contingencies
Commitments to extend credit	1,653	2,015
HELOC commitments
Loss Contingencies
Commitments to extend credit	562	558
Other consumer commitments
Loss Contingencies
Commitments to extend credit	301	175
Standby and commercial letters of credit
Loss Contingencies
Commitments to extend credit	$ 97	$ 82