Credit Quality and the Allowance for Loan and Lease Losses - Summary of Recorded Investment in Portfolio Loans and Leases by Age and Class (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Financing Receivable, Recorded Investment, Past Due
Loans and Leases	$ 105,957	$ 106,329
Commercial
Financing Receivable, Recorded Investment, Past Due
Loans and Leases	66,720	68,997
90 Days Past Due and Still Accruing	7	48
Commercial | Current
Financing Receivable, Recorded Investment, Past Due
Loans and Leases	66,515	68,640
Commercial | Total Past Due
Financing Receivable, Recorded Investment, Past Due
Loans and Leases	205	357
Commercial | 30 to 89 Days
Financing Receivable, Recorded Investment, Past Due
Loans and Leases	136	171
Commercial | 90 Days or More
Financing Receivable, Recorded Investment, Past Due
Loans and Leases	69	186
Commercial | Commercial and industrial loans
Financing Receivable, Recorded Investment, Past Due
Loans and Leases	47,834	49,665
90 Days Past Due and Still Accruing	4	39
Loans and leases related to SBA Paycheck Protection Program of CARES Act	2,300	4,800
Commercial | Commercial and industrial loans | Current
Financing Receivable, Recorded Investment, Past Due
Loans and Leases	47,682	49,421
Commercial | Commercial and industrial loans | Total Past Due
Financing Receivable, Recorded Investment, Past Due
Loans and Leases	152	244
Commercial | Commercial and industrial loans | 30 to 89 Days
Financing Receivable, Recorded Investment, Past Due
Loans and Leases	96	119
Loans and leases related to SBA Paycheck Protection Program of CARES Act	51
Commercial | Commercial and industrial loans | 90 Days or More
Financing Receivable, Recorded Investment, Past Due
Loans and Leases	56	125
Commercial | Commercial mortgage owner-occupied loans
Financing Receivable, Recorded Investment, Past Due
Loans and Leases	4,786	4,675
90 Days Past Due and Still Accruing	2	7
Commercial | Commercial mortgage owner-occupied loans | Current
Financing Receivable, Recorded Investment, Past Due
Loans and Leases	4,779	4,645
Commercial | Commercial mortgage owner-occupied loans | Total Past Due
Financing Receivable, Recorded Investment, Past Due
Loans and Leases	7	30
Commercial | Commercial mortgage owner-occupied loans | 30 to 89 Days
Financing Receivable, Recorded Investment, Past Due
Loans and Leases	0	7
Commercial | Commercial mortgage owner-occupied loans | 90 Days or More
Financing Receivable, Recorded Investment, Past Due
Loans and Leases	7	23
Commercial | Commercial mortgage nonowner-occupied loans
Financing Receivable, Recorded Investment, Past Due
Loans and Leases	5,514	5,927
90 Days Past Due and Still Accruing	0	1
Commercial | Commercial mortgage nonowner-occupied loans | Current
Financing Receivable, Recorded Investment, Past Due
Loans and Leases	5,478	5,860
Commercial | Commercial mortgage nonowner-occupied loans | Total Past Due
Financing Receivable, Recorded Investment, Past Due
Loans and Leases	36	67
Commercial | Commercial mortgage nonowner-occupied loans | 30 to 89 Days
Financing Receivable, Recorded Investment, Past Due
Loans and Leases	35	31
Commercial | Commercial mortgage nonowner-occupied loans | 90 Days or More
Financing Receivable, Recorded Investment, Past Due
Loans and Leases	1	36
Commercial | Commercial construction loans
Financing Receivable, Recorded Investment, Past Due
Loans and Leases	5,456	5,815
90 Days Past Due and Still Accruing	0	0
Commercial | Commercial construction loans | Current
Financing Receivable, Recorded Investment, Past Due
Loans and Leases	5,454	5,808
Commercial | Commercial construction loans | Total Past Due
Financing Receivable, Recorded Investment, Past Due
Loans and Leases	2	7
Commercial | Commercial construction loans | 30 to 89 Days
Financing Receivable, Recorded Investment, Past Due
Loans and Leases	2	7
Commercial | Commercial construction loans | 90 Days or More
Financing Receivable, Recorded Investment, Past Due
Loans and Leases	0	0
Commercial | Commercial leases
Financing Receivable, Recorded Investment, Past Due
Loans and Leases	3,130	2,915
90 Days Past Due and Still Accruing	1	1
Commercial | Commercial leases | Current
Financing Receivable, Recorded Investment, Past Due
Loans and Leases	3,122	2,906
Commercial | Commercial leases | Total Past Due
Financing Receivable, Recorded Investment, Past Due
Loans and Leases	8	9
Commercial | Commercial leases | 30 to 89 Days
Financing Receivable, Recorded Investment, Past Due
Loans and Leases	3	7
Commercial | Commercial leases | 90 Days or More
Financing Receivable, Recorded Investment, Past Due
Loans and Leases	$ 5	$ 2