Legal Proceedings, Contingencies and Commitments - Summary of the Contractual Amount of Significant Commitments (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Mortgage loan commitments including interest rate locks
Loss Contingencies
Commitments to extend credit	$ 7,636	$ 10,702
Warehouse loan commitments
Loss Contingencies
Commitments to extend credit	4,697	2,849
Commercial and industrial commitments
Loss Contingencies
Commitments to extend credit	1,452	1,271
Other construction commitments
Loss Contingencies
Commitments to extend credit	2,429	1,934
HELOC commitments
Loss Contingencies
Commitments to extend credit	603	544
Other consumer commitments
Loss Contingencies
Commitments to extend credit	151	121
Standby and commercial letters of credit
Loss Contingencies
Commitments to extend credit	$ 107	$ 95