Loans and Allowance for Loan Losses - Nonaccural Loans (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Nonaccrual loans
Nonaccrual loans	$ 552	$ 375
Nonaccrual loans, before purchased credit-impaired loans	546	366
Troubled debt restructured loans that continue to accrue interest	413	283
Troubled debt restructured nonaccrual loans (included in the total nonaccrual loans above)	409	184
Commercial portfolio
Nonaccrual loans
Nonaccrual loans	321	95
Commercial portfolio | Commercial and industrial
Nonaccrual loans
Nonaccrual loans	284	55
Commercial portfolio | Commercial mortgage
Nonaccrual loans
Nonaccrual loans	37	40
Consumer portfolio
Nonaccrual loans
Nonaccrual loans	225	271
Consumer portfolio | Residential mortgage
Nonaccrual loans
Nonaccrual loans	190	231
Consumer portfolio | Home equity and other consumer loans
Nonaccrual loans
Nonaccrual loans	35	40
Purchased credit-impaired loans
Nonaccrual loans
Nonaccrual loans	$ 6	$ 9