Loans and Allowance for Loan Losses (Details 4) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Nonaccrual loans
Nonaccrual loans, before purchased credit-impaired loans	$ 411	$ 366
Nonaccrual loans	419	375
Troubled debt restructured loans that continue to accrue interest	264	283
Troubled debt restructured nonaccrual loans (included in the total nonaccrual loans above)	202	184
Commercial portfolio
Nonaccrual loans
Nonaccrual loans	178	95
Commercial portfolio | Commercial and industrial
Nonaccrual loans
Nonaccrual loans	138	55
Commercial portfolio | Commercial mortgage
Nonaccrual loans
Nonaccrual loans	40	40
Consumer portfolio
Nonaccrual loans
Nonaccrual loans	233	271
Consumer portfolio | Residential mortgage
Nonaccrual loans
Nonaccrual loans	201	231
Consumer portfolio | Home equity and other consumer loans
Nonaccrual loans
Nonaccrual loans	32	40
Purchased credit-impaired loans
Nonaccrual loans
Nonaccrual loans	$ 8	$ 9