Credit Quality and the Allowance for Loan and Lease Losses - Summary of Loans Modified in a TDR (Details) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2021 USD ($) loan	Sep. 30, 2020 USD ($) loan	Sep. 30, 2021 USD ($) loan	Sep. 30, 2020 USD ($) loan
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period \| loan	2,400	1,237	8,190	4,577
Amortized Cost Basis of Loans Modified in a TDR During the Period	$ 67	$ 129	$ 262	$ 422
Increase (Decrease) to ALLL Upon Modification	1	(5)	8	26
Charge-offs Recognized Upon Modification	$ 0	$ 8	$ 0	$ 8
Commercial \| Commercial and industrial loans
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period \| loan	29	33	55	96
Amortized Cost Basis of Loans Modified in a TDR During the Period	$ 23	$ 75	$ 54	$ 250
Increase (Decrease) to ALLL Upon Modification	(1)	1	0	25
Charge-offs Recognized Upon Modification	$ 0	$ 7	$ 0	$ 7
Commercial \| Commercial mortgage owner-occupied loans
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period \| loan	3	10	4	38
Amortized Cost Basis of Loans Modified in a TDR During the Period	$ 1	$ 19	$ 6	$ 38
Increase (Decrease) to ALLL Upon Modification	0	(3)	0	(3)
Charge-offs Recognized Upon Modification	$ 0	$ 0	$ 0	$ 0
Commercial \| Commercial mortgage nonowner-occupied loans
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period \| loan	1	3	4	15
Amortized Cost Basis of Loans Modified in a TDR During the Period	$ 0	$ 16	$ 26	$ 38
Increase (Decrease) to ALLL Upon Modification	0	(2)	0	(2)
Charge-offs Recognized Upon Modification	$ 0	$ 0	$ 0	$ 0
Commercial \| Commercial construction
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period \| loan				3
Amortized Cost Basis of Loans Modified in a TDR During the Period				$ 21
Increase (Decrease) to ALLL Upon Modification				1
Charge-offs Recognized Upon Modification				$ 0
Residential Mortgage
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period \| loan	98	66	400	359
Amortized Cost Basis of Loans Modified in a TDR During the Period	$ 15	$ 11	$ 74	$ 48
Increase (Decrease) to ALLL Upon Modification	1	0	3	1
Charge-offs Recognized Upon Modification	$ 0	$ 0	$ 0	$ 0
Consumer \| Home equity
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period \| loan	54	88	151	130
Amortized Cost Basis of Loans Modified in a TDR During the Period	$ 3	$ 2	$ 8	$ 6
Increase (Decrease) to ALLL Upon Modification	(1)	(3)	(2)	(4)
Charge-offs Recognized Upon Modification	$ 0	$ 0	$ 0	$ 0
Consumer \| Indirect secured consumer loans
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period \| loan	1,045	14	3,238	56
Amortized Cost Basis of Loans Modified in a TDR During the Period	$ 19	$ 0	$ 70	$ 0
Increase (Decrease) to ALLL Upon Modification	0	0	1	0
Charge-offs Recognized Upon Modification	$ 0	$ 0	$ 0	$ 0
Consumer \| Credit card
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period \| loan	1,170	1,023	4,338	3,880
Amortized Cost Basis of Loans Modified in a TDR During the Period	$ 6	$ 6	$ 24	$ 21
Increase (Decrease) to ALLL Upon Modification	2	2	6	8
Charge-offs Recognized Upon Modification	$ 0	$ 1	$ 0	$ 1

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=124255953&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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