Loans and Allowance for Loan Losses - Summary of Nonaccrual Loans (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Nonaccrual loans
Nonaccrual loans	$ 591	$ 328
Troubled debt restructured loans that continue to accrue interest	322	392
Troubled debt restructured nonaccrual loans (included in the total nonaccrual loans above)	198	171
Commercial
Nonaccrual loans
Nonaccrual loans	398	190
Consumer
Nonaccrual loans
Nonaccrual loans	193	138
Residential mortgage and home equity | Consumer Loans
Nonaccrual loans
Nonaccrual loans	191	137
Other consumer | Consumer Loans
Nonaccrual loans
Nonaccrual loans	2	1
Commercial mortgage | Commercial Loans
Nonaccrual loans
Nonaccrual loans	178	15
Construction | Commercial Loans
Nonaccrual loans
Nonaccrual loans	44
Commercial and industrial | Commercial Loans
Nonaccrual loans
Nonaccrual loans	$ 176	175
Construction | Commercial Loans
Nonaccrual loans
Nonaccrual loans		$ 0