Loans and Allowance for Loan Losses - Nonaccural Loans (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Nonaccrual loans
Nonaccrual loans	$ 689	$ 552
Nonaccrual loans, before purchased credit-impaired loans	685	546
Troubled debt restructured loans that continue to accrue interest	215	413
Troubled debt restructured nonaccrual loans (included in total nonaccrual loans above)	384	409
Commercial
Nonaccrual loans
Nonaccrual loans	488	321
Commercial | Commercial and industrial
Nonaccrual loans
Nonaccrual loans	457	284
Commercial | Commercial mortgage
Nonaccrual loans
Nonaccrual loans	31	37
Consumer
Nonaccrual loans
Nonaccrual loans	197	225
Consumer | Residential mortgage
Nonaccrual loans
Nonaccrual loans	171	190
Consumer | Home equity and other consumer loans
Nonaccrual loans
Nonaccrual loans	26	35
Purchased Credit- Impaired
Nonaccrual loans
Nonaccrual loans	$ 4	$ 6