Loans and Leases - Composition of Loan and Lease Portfolio (Parenthetical) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2020		Sep. 30, 2021
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 42,822		$ 43,631
Deferred loan origination fees		2
Other Assets
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accrued interest receivable		219		207
Lease Financing, Unearned Income
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unearned income		116		98
Non-Covered Loans		1,735		1,768
Commercial and Industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans	[2]	3,417	[1]	3,704	[3]
Commercial and Industrial | Other Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		1,682		1,936
Commercial and Industrial | Specialty Finance Loans | Other Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		3,000		3,100
Commercial and Industrial | Other Commercial and Industrial Loans | Other Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 393		$ 561

[1] Includes lease financing receivables, all of which were classified as Pass.

[2] Includes specialty finance loans and leases of $3.1 billion and $3.0 billion, respectively, at September 30, 2021 and December 31, 2020, and other C&I loans of $561 million and $393 million, respectively, at September 30, 2021 and December 31, 2020.

[3] Includes lease financing receivables, all of which were classified as Pass.