Loans and Leases - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2021		Sep. 30, 2020	Sep. 30, 2021		Sep. 30, 2020	Jun. 30, 2021	Dec. 31, 2020		Jun. 30, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable
Unearned income	$ 253			$ 253				$ 280
Net premium	444			444				251
Accrued interest receivable	358			358				350
Loans pledged at the FHLB	15,500			15,500				15,500
Loans pledged at the FRB	45,100			45,100				37,800
Direct financing lease - interest income	10		$ 16	33		$ 50
Sales type lease - interest income	11		7	31		20
Allowance for loan and lease losses	1,954	[1]	$ 2,574	1,954	[1]	$ 2,574	$ 2,033	2,453	[1]	$ 2,696	$ 1,202
Commercial Leases
Accounts, Notes, Loans and Financing Receivable
Allowance for loan and lease losses	$ 21			$ 21				$ 29

[1] Includes $27 and $55 of other short-term investments, $383 and $756 of portfolio loans and leases, $(3) and $(7) of ALLL, $2 and $5 of other assets, $1 and $2 of other liabilities, and $325 and $656 of long-term debt from consolidated VIEs that are included in their respective captions above at September 30, 2021 and December 31, 2020, respectively. For further information, refer to Note 12.