Credit Quality and the Allowance for Loan and Lease Losses - Summary of Loans Modified in a TDR (Details) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2021 USD ($) loan	Jun. 30, 2020 USD ($) loan	Jun. 30, 2021 USD ($) loan	Jun. 30, 2020 USD ($) loan
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period \| loan	1,993	1,184	5,790	3,340
Amortized Cost Basis of Loans Modified in a TDR During the Period	$ 66	$ 174	$ 193	$ 294
Increase (Decrease) to ALLL Upon Modification	2	18	7	31
Charge-offs Recognized Upon Modification	$ 0	$ 0	$ 0	$ 0
Commercial \| Commercial and industrial loans
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period \| loan	7	33	26	63
Amortized Cost Basis of Loans Modified in a TDR During the Period	$ 25	$ 107	$ 31	$ 176
Increase (Decrease) to ALLL Upon Modification	0	14	1	24
Charge-offs Recognized Upon Modification	$ 0	$ 0	$ 0	$ 0
Commercial \| Commercial mortgage owner-occupied loans
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period \| loan		17	1	28
Amortized Cost Basis of Loans Modified in a TDR During the Period		$ 12	$ 4	$ 19
Increase (Decrease) to ALLL Upon Modification		0	0	0
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 Period \| loan		9	3	12
Amortized Cost Basis of Loans Modified in a TDR During the Period		$ 14	$ 25	$ 22
Increase (Decrease) to ALLL Upon Modification		0	0	0
Charge-offs Recognized Upon Modification		$ 0	$ 0	$ 0
Commercial \| Commercial construction
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period \| loan		2		3
Amortized Cost Basis of Loans Modified in a TDR During the Period		$ 21		$ 21
Increase (Decrease) to ALLL Upon Modification		1		1
Charge-offs Recognized Upon Modification		$ 0		$ 0
Residential Mortgage
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period \| loan	124	109	302	293
Amortized Cost Basis of Loans Modified in a TDR During the Period	$ 23	$ 13	$ 59	$ 37
Increase (Decrease) to ALLL Upon Modification	1	1	2	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	39	21	97	42
Amortized Cost Basis of Loans Modified in a TDR During the Period	$ 2	$ 2	$ 5	$ 4
Increase (Decrease) to ALLL Upon Modification	0	0	(1)	(1)
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	450	20	2,193	42
Amortized Cost Basis of Loans Modified in a TDR During the Period	$ 8	$ 0	$ 51	$ 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	1,373	973	3,168	2,857
Amortized Cost Basis of Loans Modified in a TDR During the Period	$ 8	$ 5	$ 18	$ 15
Increase (Decrease) to ALLL Upon Modification	1	2	4	6
Charge-offs Recognized Upon Modification	$ 0	$ 0	$ 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=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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