Loans and Allowance for Loan Losses - Summary of Nonaccrual Loans (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Nonaccrual loans
Nonaccrual loans	$ 621	$ 328
Troubled debt restructured loans that continue to accrue interest	317	392
Troubled debt restructured nonaccrual loans (included in the total nonaccrual loans above)	253	171
Commercial
Nonaccrual loans
Nonaccrual loans	414	190
Consumer
Nonaccrual loans
Nonaccrual loans	207	138
Residential mortgage and home equity | Consumer Loans
Nonaccrual loans
Nonaccrual loans	206	137
Other consumer | Consumer Loans
Nonaccrual loans
Nonaccrual loans	1	1
Commercial mortgage | Commercial Loans
Nonaccrual loans
Nonaccrual loans	147	15
Construction | Commercial Loans
Nonaccrual loans
Nonaccrual loans	45
Commercial and industrial | Commercial Loans
Nonaccrual loans
Nonaccrual loans	$ 222	175
Construction | Commercial Loans
Nonaccrual loans
Nonaccrual loans		$ 0