Loans and ACL - Types of Modifications and Impact to Allowance (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Newly Designated TDRs | Commercial: | Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
ALLL at Period End	$ 1	$ 4	$ 3	$ 7
Financing Receivable, Troubled Debt Restructuring, Premodification	12	27	48	46
Newly Designated TDRs | Commercial: | CRE
Financing Receivable, Troubled Debt Restructuring [Line Items]
ALLL at Period End	2	0	2	0
Financing Receivable, Troubled Debt Restructuring, Premodification	16	1	17	4
Newly Designated TDRs | Commercial: | Commercial construction
Financing Receivable, Troubled Debt Restructuring [Line Items]
ALLL at Period End		0		0
Financing Receivable, Troubled Debt Restructuring, Premodification		0		0
Newly Designated TDRs | Commercial: | Lease financing
Financing Receivable, Troubled Debt Restructuring [Line Items]
ALLL at Period End	0	0	0	0
Financing Receivable, Troubled Debt Restructuring, Premodification	0	0	1	0
Newly Designated TDRs | Consumer: | Residential Mortgage
Financing Receivable, Troubled Debt Restructuring [Line Items]
ALLL at Period End	5	4	10	10
Financing Receivable, Troubled Debt Restructuring, Premodification	105	52	199	127
Newly Designated TDRs | Consumer: | Residential home equity and direct
Financing Receivable, Troubled Debt Restructuring [Line Items]
ALLL at Period End	0	0	1	1
Financing Receivable, Troubled Debt Restructuring, Premodification	16	2	39	5
Newly Designated TDRs | Consumer: | Indirect auto
Financing Receivable, Troubled Debt Restructuring [Line Items]
ALLL at Period End	7	10	12	21
Financing Receivable, Troubled Debt Restructuring, Premodification	31	52	104	103
Newly Designated TDRs | Consumer: | Indirect other
Financing Receivable, Troubled Debt Restructuring [Line Items]
ALLL at Period End	0	0	0	0
Financing Receivable, Troubled Debt Restructuring, Premodification	1	1	2	2
Newly Designated TDRs | Consumer: | Student
Financing Receivable, Troubled Debt Restructuring [Line Items]
ALLL at Period End	0	0	0	0
Financing Receivable, Troubled Debt Restructuring, Premodification	3	0	4	0
Newly Designated TDRs | Credit card
Financing Receivable, Troubled Debt Restructuring [Line Items]
ALLL at Period End	3	2	6	5
Financing Receivable, Troubled Debt Restructuring, Premodification	7	5	17	11
Newly Designated TDRs | Rate | Commercial: | Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs	5	24	33	50
Newly Designated TDRs | Rate | Commercial: | CRE
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs	23	0	24	1
Newly Designated TDRs | Rate | Commercial: | Commercial construction
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs		0		0
Newly Designated TDRs | Rate | Commercial: | Lease financing
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs	0	0	1	0
Newly Designated TDRs | Rate | Consumer: | Residential Mortgage
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs	67	49	144	122
Newly Designated TDRs | Rate | Consumer: | Residential home equity and direct
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs	11	2	28	5
Newly Designated TDRs | Rate | Consumer: | Indirect auto
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs	22	49	78	96
Newly Designated TDRs | Rate | Consumer: | Indirect other
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs	1	1	2	2
Newly Designated TDRs | Rate | Consumer: | Student
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs	0	0	0	0
Newly Designated TDRs | Rate | Credit card
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs	8	5	18	11
Newly Designated TDRs | Structure | Commercial: | Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs	1	3	4	6
Newly Designated TDRs | Structure | Commercial: | CRE
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs	1	1	1	1
Newly Designated TDRs | Structure | Commercial: | Commercial construction
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	0	0	0
Newly Designated TDRs | Structure | Consumer: | Residential Mortgage
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs	32	6	47	14
Newly Designated TDRs | Structure | Consumer: | Residential home equity and direct
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs	5	1	10	2
Newly Designated TDRs | Structure | Consumer: | Indirect auto
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs	8	1	22	2
Newly Designated TDRs | Structure | Consumer: | Indirect other
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs	0	0	0	0
Newly Designated TDRs | Structure | Consumer: | Student
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs	3	0	4	0
Newly Designated TDRs | Structure | Credit card
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs	0	0	0	0
Re-Modification of Previously Designated TDRs | Rate
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs	8	14	26	37
Re-Modification of Previously Designated TDRs | Structure
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs	$ 5	$ 11	$ 6	$ 16