Allowance for Credit Losses and Reserve for Unfunded Lending Commitments - Additional Information (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for credit loss	$ 11,573		$ 15,564
Allowance for credit losses
Accounts, Notes, Loans and Financing Receivable [Line Items]
Increase (Decrease) in Allowance for Credit Loss	(4,000)
Allowance for credit loss	$ 11,573	$ 12,346	$ 15,564	$ 16,129	$ 16,832	$ 7,208