Outstanding Loans and Leases and Allowance for Credit Losses - Credit Quality Indicators, Narrative (Details) - USD ($) $ in Billions	Sep. 30, 2021	Dec. 31, 2020
Receivables [Abstract]
Commercial reservable criticized utilized exposure, amount	$ 24.1	$ 38.7
Commercial reservable criticized utilized exposure, percent	4.53%	7.31%