Loans and ACL - Types of Modifications and Impact to Allowance (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Newly Designated TDRs [Member] | Commercial | Commercial and industrial
Financing Receivable, Modifications [Line Items]
Impact To ALLL	$ 0	$ 1
Newly Designated TDRs [Member] | Commercial | CRE
Financing Receivable, Modifications [Line Items]
Impact To ALLL	0	0
Newly Designated TDRs [Member] | Commercial | Lease financing
Financing Receivable, Modifications [Line Items]
Impact To ALLL	0	0
Newly Designated TDRs [Member] | Retail | Residential mortgage
Financing Receivable, Modifications [Line Items]
Impact To ALLL	5	6
Newly Designated TDRs [Member] | Retail | Direct
Financing Receivable, Modifications [Line Items]
Impact To ALLL	0	0
Newly Designated TDRs [Member] | Retail | Indirect
Financing Receivable, Modifications [Line Items]
Impact To ALLL	5	4
Newly Designated TDRs [Member] | Revolving credit
Financing Receivable, Modifications [Line Items]
Impact To ALLL	1	1
Newly Designated TDRs [Member] | Rate | Commercial | Commercial and industrial
Financing Receivable, Modifications [Line Items]
TDRs	10	22
Newly Designated TDRs [Member] | Rate | Commercial | CRE
Financing Receivable, Modifications [Line Items]
TDRs	19	6
Newly Designated TDRs [Member] | Rate | Commercial | Lease financing
Financing Receivable, Modifications [Line Items]
TDRs	0	0
Newly Designated TDRs [Member] | Rate | Retail | Residential mortgage
Financing Receivable, Modifications [Line Items]
TDRs	82	128
Newly Designated TDRs [Member] | Rate | Retail | Direct
Financing Receivable, Modifications [Line Items]
TDRs	2	3
Newly Designated TDRs [Member] | Rate | Retail | Indirect
Financing Receivable, Modifications [Line Items]
TDRs	42	41
Newly Designated TDRs [Member] | Rate | Revolving credit
Financing Receivable, Modifications [Line Items]
TDRs	5	5
Newly Designated TDRs [Member] | Structure | Commercial | Commercial and industrial
Financing Receivable, Modifications [Line Items]
TDRs	10	31
Newly Designated TDRs [Member] | Structure | Commercial | CRE
Financing Receivable, Modifications [Line Items]
TDRs	1	2
Newly Designated TDRs [Member] | Structure | Commercial | Lease financing
Financing Receivable, Modifications [Line Items]
TDRs	0	0
Newly Designated TDRs [Member] | Structure | Retail | Residential mortgage
Financing Receivable, Modifications [Line Items]
TDRs	10	6
Newly Designated TDRs [Member] | Structure | Retail | Direct
Financing Receivable, Modifications [Line Items]
TDRs	0	1
Newly Designated TDRs [Member] | Structure | Retail | Indirect
Financing Receivable, Modifications [Line Items]
TDRs	1	2
Newly Designated TDRs [Member] | Structure | Revolving credit
Financing Receivable, Modifications [Line Items]
TDRs	0	0
Re-Modification of Previously Designated TDRs [Member]
Financing Receivable, Modifications [Line Items]
Impact To ALLL	0	0
Re-Modification of Previously Designated TDRs [Member] | Rate
Financing Receivable, Modifications [Line Items]
TDRs	21	45
Re-Modification of Previously Designated TDRs [Member] | Structure
Financing Receivable, Modifications [Line Items]
TDRs	$ 5	$ 9