Credit Quality and the Allowance for Loan and Lease Losses - Summary of Loans Modified in a TDR (Details) $ in Millions	12 Months Ended
Dec. 31, 2020 USD ($) loan	Dec. 31, 2019 USD ($) loan	Dec. 31, 2018 USD ($) loan
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Year \| loan	6,531	7,056	8,869
Recorded Investment in Loans Modified in a TDR During the Year	$ 525	$ 374	$ 415
Increase (Decrease) to ALLL Upon Modification	22	(10)	13
Charge-offs Recognized Upon Modification	$ 8	$ 8	$ 9
Commercial \| Commercial and industrial loans
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Year \| loan	124	97	54
Recorded Investment in Loans Modified in a TDR During the Year	$ 305	$ 223	$ 200
Increase (Decrease) to ALLL Upon Modification	26	(19)	1
Charge-offs Recognized Upon Modification	$ 7	$ 5	$ 7
Commercial \| Commercial mortgage owner-occupied loans
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Year \| loan	43	15	6
Recorded Investment in Loans Modified in a TDR During the Year	$ 58	$ 12	$ 3
Increase (Decrease) to ALLL Upon Modification	(11)	0	(1)
Charge-offs Recognized Upon Modification	$ 0	$ 0	$ 0
Commercial \| Commercial mortgage nonowner-occupied loans
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Year \| loan	19	1	3
Recorded Investment in Loans Modified in a TDR During the Year	$ 44	$ 0	$ 0
Increase (Decrease) to ALLL Upon Modification	(2)	0	0
Charge-offs Recognized Upon Modification	$ 0	$ 0	$ 0
Commercial \| Commercial construction loans
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Year \| loan	3
Recorded Investment in Loans Modified in a TDR During the Year	$ 21
Increase (Decrease) to ALLL Upon Modification	1
Charge-offs Recognized Upon Modification	$ 0
Residential Mortgage Loans
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Year \| loan	424	722	1,128
Recorded Investment in Loans Modified in a TDR During the Year	$ 58	$ 101	$ 168
Increase (Decrease) to ALLL Upon Modification	1	1	4
Charge-offs Recognized Upon Modification	$ 0	$ 0	$ 0
Consumer Portfolio Segment \| Home equity
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Year \| loan	147	80	111
Recorded Investment in Loans Modified in a TDR During the Year	$ 7	$ 4	$ 7
Increase (Decrease) to ALLL Upon Modification	(4)	0	0
Charge-offs Recognized Upon Modification	$ 0	$ 0	$ 0
Consumer Portfolio Segment \| Indirect secured consumer loans
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Year \| loan	70	100	84
Recorded Investment in Loans Modified in a TDR During the Year	$ 0	$ 0	$ 0
Increase (Decrease) to ALLL Upon Modification	0	0	0
Charge-offs Recognized Upon Modification	$ 0	$ 0	$ 0
Consumer Portfolio Segment \| Credit card
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Year \| loan	5,701	6,041	7,483
Recorded Investment in Loans Modified in a TDR During the Year	$ 32	$ 34	$ 37
Increase (Decrease) to ALLL Upon Modification	11	8	9
Charge-offs Recognized Upon Modification	$ 1	$ 3	$ 2

Amount of credit loss expense (reversal of expense) for financing receivable from change in methodology.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 11
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919244-210447

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Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
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