Loans and ACL - Types of Modifications and Impact to Allowance (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Newly Designated TDRs | Commercial: | Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
ALLL at Period End	$ 2	$ 3
Financing Receivable, Troubled Debt Restructuring, Premodification	36	19
Newly Designated TDRs | Commercial: | CRE
Financing Receivable, Troubled Debt Restructuring [Line Items]
ALLL at Period End	0	0
Financing Receivable, Troubled Debt Restructuring, Premodification	1	3
Newly Designated TDRs | Commercial: | Lease financing
Financing Receivable, Troubled Debt Restructuring [Line Items]
ALLL at Period End	0
Financing Receivable, Troubled Debt Restructuring, Premodification	1
Newly Designated TDRs | Consumer: | Residential Mortgage
Financing Receivable, Troubled Debt Restructuring [Line Items]
ALLL at Period End	5	6
Financing Receivable, Troubled Debt Restructuring, Premodification	94	75
Newly Designated TDRs | Consumer: | Residential home equity and direct
Financing Receivable, Troubled Debt Restructuring [Line Items]
ALLL at Period End	1	1
Financing Receivable, Troubled Debt Restructuring, Premodification	23	3
Newly Designated TDRs | Consumer: | Indirect auto
Financing Receivable, Troubled Debt Restructuring [Line Items]
ALLL at Period End	5	11
Financing Receivable, Troubled Debt Restructuring, Premodification	73	51
Newly Designated TDRs | Consumer: | Indirect other
Financing Receivable, Troubled Debt Restructuring [Line Items]
ALLL at Period End	0	0
Financing Receivable, Troubled Debt Restructuring, Premodification	1	1
Newly Designated TDRs | Consumer: | Student
Financing Receivable, Troubled Debt Restructuring [Line Items]
ALLL at Period End	0
Financing Receivable, Troubled Debt Restructuring, Premodification	1
Newly Designated TDRs | Credit card
Financing Receivable, Troubled Debt Restructuring [Line Items]
ALLL at Period End	3	3
Financing Receivable, Troubled Debt Restructuring, Premodification	10	6
Newly Designated TDRs | Rate | Commercial: | Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs	28	26
Newly Designated TDRs | Rate | Commercial: | CRE
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs	1	1
Newly Designated TDRs | Rate | Commercial: | Lease financing
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs	1
Newly Designated TDRs | Rate | Consumer: | Residential Mortgage
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs	77	73
Newly Designated TDRs | Rate | Consumer: | Residential home equity and direct
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs	17	3
Newly Designated TDRs | Rate | Consumer: | Indirect auto
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs	56	47
Newly Designated TDRs | Rate | Consumer: | Indirect other
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs	1	1
Newly Designated TDRs | Rate | Consumer: | Student
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs	0
Newly Designated TDRs | Rate | Credit card
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs	10	6
Newly Designated TDRs | Structure | Commercial: | Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs	3	3
Newly Designated TDRs | Structure | Commercial: | CRE
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs	0	0
Newly Designated TDRs | Structure | Commercial: | Lease financing
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs	0
Newly Designated TDRs | Structure | Consumer: | Residential Mortgage
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs	15	8
Newly Designated TDRs | Structure | Consumer: | Residential home equity and direct
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs	5	1
Newly Designated TDRs | Structure | Consumer: | Indirect auto
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs	14	1
Newly Designated TDRs | Structure | Consumer: | Indirect other
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs	0	0
Newly Designated TDRs | Structure | Consumer: | Student
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs	1
Newly Designated TDRs | Structure | Credit card
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs	0	0
Re-Modification of Previously Designated TDRs | Rate
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs	18	23
Re-Modification of Previously Designated TDRs | Structure
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs	$ 1	$ 5