Loans and Allowance for Loan Losses - Nonaccural Loans (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Nonaccrual loans
Nonaccrual loans	$ 421	$ 465
Troubled debt restructured loans that continue to accrue interest	299	348
Troubled debt restructured nonaccrual loans (included in total nonaccrual loans above)	136	229
Commercial
Nonaccrual loans
Nonaccrual loans	281	339
Commercial | Commercial and industrial
Nonaccrual loans
Nonaccrual loans	269	319
Commercial | Commercial mortgage
Nonaccrual loans
Nonaccrual loans	12	20
Consumer
Nonaccrual loans
Nonaccrual loans	140	126
Consumer | Residential mortgage
Nonaccrual loans
Nonaccrual loans	121	104
Consumer | Home equity and other consumer loans
Nonaccrual loans
Nonaccrual loans	$ 19	$ 22