Credit Quality and the Allowance for Loan and Lease Losses - Summary of Loans Modified in a TDR (Details) $ in Millions	3 Months Ended
Mar. 31, 2021 USD ($) loan	Mar. 31, 2020 USD ($) loan
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period \| loan	3,797	2,156
Amortized Cost Basis of Loans Modified in a TDR During the Period	$ 127	$ 120
Increase (Decrease) to ALLL Upon Modification	5	13
Charge-offs Recognized Upon Modification	$ 0	$ 0
Commercial \| Commercial and industrial loans
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period \| loan	19	30
Amortized Cost Basis of Loans Modified in a TDR During the Period	$ 6	$ 69
Increase (Decrease) to ALLL Upon Modification	1	10
Charge-offs Recognized Upon Modification	$ 0	$ 0
Commercial \| Commercial mortgage owner-occupied loans
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period \| loan	1	11
Amortized Cost Basis of Loans Modified in a TDR During the Period	$ 4	$ 7
Increase (Decrease) to ALLL Upon Modification	0	0
Charge-offs Recognized Upon Modification	$ 0	$ 0
Commercial \| Commercial mortgage nonowner-occupied loans
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period \| loan	3	3
Amortized Cost Basis of Loans Modified in a TDR During the Period	$ 25	$ 8
Increase (Decrease) to ALLL Upon Modification	0	0
Charge-offs Recognized Upon Modification	$ 0	$ 0
Commercial \| Commercial construction
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period \| loan		1
Amortized Cost Basis of Loans Modified in a TDR During the Period		$ 0
Increase (Decrease) to ALLL Upon Modification		0
Charge-offs Recognized Upon Modification		$ 0
Residential Mortgage
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period \| loan	178	184
Amortized Cost Basis of Loans Modified in a TDR During the Period	$ 36	$ 24
Increase (Decrease) to ALLL Upon Modification	1	0
Charge-offs Recognized Upon Modification	$ 0	$ 0
Consumer \| Home equity
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period \| loan	58	21
Amortized Cost Basis of Loans Modified in a TDR During the Period	$ 3	$ 2
Increase (Decrease) to ALLL Upon Modification	(1)	(1)
Charge-offs Recognized Upon Modification	$ 0	$ 0
Consumer \| Indirect secured consumer loans
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period \| loan	1,743	22
Amortized Cost Basis of Loans Modified in a TDR During the Period	$ 43	$ 0
Increase (Decrease) to ALLL Upon Modification	1	0
Charge-offs Recognized Upon Modification	$ 0	$ 0
Consumer \| Credit card
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period \| loan	1,795	1,884
Amortized Cost Basis of Loans Modified in a TDR During the Period	$ 10	$ 10
Increase (Decrease) to ALLL Upon Modification	3	4
Charge-offs Recognized Upon Modification	$ 0	$ 0

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
-URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953676-111524

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