Premises, Equipment, and Leases - Maturity of Lease Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Abstract]
2021	$ 52
2022	49
2023	44
2024	40
2025	38
2026 and thereafter	257
Total lease payments	480
Less lease liability interest	(69)
Total	$ 411	$ 226