Loans and Allowance for Loan Losses - Summary of Nonaccrual Loans (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Nonaccrual loans
Nonaccrual loans	$ 465	$ 689
Troubled debt restructured loans that continue to accrue interest	308	215
Troubled debt restructured nonaccrual loans (included in the total nonaccrual loans above)	224	384
Commercial
Nonaccrual loans
Nonaccrual loans	330	489
Consumer
Nonaccrual loans
Nonaccrual loans	135	200
Commercial and industrial | Commercial
Nonaccrual loans
Nonaccrual loans	308	458
Commercial mortgage | Commercial
Nonaccrual loans
Nonaccrual loans	22	31
Residential mortgage | Consumer
Nonaccrual loans
Nonaccrual loans	112	171
Home equity and other consumer loans | Consumer
Nonaccrual loans
Nonaccrual loans	$ 23	$ 29