Loans and Allowance for Loan Losses - Nonaccural Loans (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Nonaccrual loans
Nonaccrual loans	$ 465	$ 689
Troubled debt restructured loans that continue to accrue interest	348	215
Troubled debt restructured nonaccrual loans (included in total nonaccrual loans above)	229	384
Commercial
Nonaccrual loans
Nonaccrual loans	339	489
Commercial | Commercial and industrial
Nonaccrual loans
Nonaccrual loans	319	458
Commercial | Commercial mortgage
Nonaccrual loans
Nonaccrual loans	20	31
Consumer
Nonaccrual loans
Nonaccrual loans	126	200
Consumer | Residential mortgage
Nonaccrual loans
Nonaccrual loans	104	171
Consumer | Home equity and other consumer loans
Nonaccrual loans
Nonaccrual loans	$ 22	$ 29