Loans and Allowance for Loan Losses - Summary of Nonaccrual Loans (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Nonaccrual loans
Nonaccrual loans	$ 680	$ 711
Troubled debt restructured loans that continue to accrue interest	207	212
Troubled debt restructured nonaccrual loans (included in the total nonaccrual loans above)	256	279
Commercial
Nonaccrual loans
Nonaccrual loans	530	527
Consumer
Nonaccrual loans
Nonaccrual loans	150	184
Residential mortgage and home equity | Consumer Loans
Nonaccrual loans
Nonaccrual loans	150	183
Other consumer | Consumer Loans
Nonaccrual loans
Nonaccrual loans	0	1
Commercial mortgage | Commercial Loans
Nonaccrual loans
Nonaccrual loans	232	317
Construction | Commercial Loans
Nonaccrual loans
Nonaccrual loans	0
Commercial and industrial | Commercial Loans
Nonaccrual loans
Nonaccrual loans	$ 298	182
Construction | Commercial Loans
Nonaccrual loans
Nonaccrual loans		$ 28