Credit Quality - Summary of Loans Modified in a TDR (Details) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)
Financing Receivable, Modifications [Line Items]
Number of Loans Modified in a TDR During the Period	1,802	1,803	4,982	6,347
Recorded Investment in Loans Modified in a TDR During the Period	$ 121	$ 86	$ 279	$ 368
Increase (Decrease) to ALLL Upon Modification	2	(4)	(8)	12
Charge-offs Recognized Upon Modification	$ 1	$ 7	$ 8	$ 8
Commercial Portfolio Segment \| Commercial and Industrial Loans
Financing Receivable, Modifications [Line Items]
Number of Loans Modified in a TDR During the Period	27	16	65	41
Recorded Investment in Loans Modified in a TDR During the Period	$ 72	$ 52	$ 168	$ 187
Increase (Decrease) to ALLL Upon Modification	(1)	(7)	(15)	2
Charge-offs Recognized Upon Modification	$ 0	$ 7	$ 5	$ 7
Commercial Portfolio Segment \| Commercial Mortgage Loans, Owner-occupied
Financing Receivable, Modifications [Line Items]
Number of Loans Modified in a TDR During the Period	4		13	2
Recorded Investment in Loans Modified in a TDR During the Period	$ 1		$ 10	$ 0
Increase (Decrease) to ALLL Upon Modification	0		0	0
Charge-offs Recognized Upon Modification	$ 0		$ 0	$ 0
Residential Mortgage Loans
Financing Receivable, Modifications [Line Items]
Number of Loans Modified in a TDR During the Period	256	185	531	969
Recorded Investment in Loans Modified in a TDR During the Period	$ 39	$ 24	$ 74	$ 148
Increase (Decrease) to ALLL Upon Modification	1	1	1	4
Charge-offs Recognized Upon Modification	$ 0	$ 0	$ 0	$ 0
Consumer Portfolio Segment \| Home Equity
Financing Receivable, Modifications [Line Items]
Number of Loans Modified in a TDR During the Period	21	30	58	84
Recorded Investment in Loans Modified in a TDR During the Period	$ 1	$ 2	$ 3	$ 6
Increase (Decrease) to ALLL Upon Modification	0	0	0	0
Charge-offs Recognized Upon Modification	$ 0	$ 0	$ 0	$ 0
Consumer Portfolio Segment \| Indirect secured consumer loans
Financing Receivable, Modifications [Line Items]
Number of Loans Modified in a TDR During the Period	27	25	65	64
Recorded Investment in Loans Modified in a TDR During the Period	$ 0	$ 0	$ 0	$ 0
Increase (Decrease) to ALLL Upon Modification	0	0	0	0
Charge-offs Recognized Upon Modification	$ 0	$ 0	$ 0	$ 0
Consumer Portfolio Segment \| Credit Card
Financing Receivable, Modifications [Line Items]
Number of Loans Modified in a TDR During the Period	1,467	1,547	4,250	5,187
Recorded Investment in Loans Modified in a TDR During the Period	$ 8	$ 8	$ 24	$ 27
Increase (Decrease) to ALLL Upon Modification	2	2	6	6
Charge-offs Recognized Upon Modification	$ 1	$ 0	$ 3	$ 1

Amount of other addition (reduction) in allowance reserve for credit loss.

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