Allowance for Credit Losses and Reserve for Unfunded Lending Commitments - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for credit loss	$ 14,017	$ 15,564
Allowance for credit losses
Accounts, Notes, Loans and Financing Receivable [Line Items]
Increase (Decrease) in Allowance for Credit Loss	(1,500)
Allowance for credit loss	$ 14,017	$ 15,564	$ 14,073	$ 7,208