Allowance for Credit Losses and Reserve for Unfunded Lending Commitments - Summary of Loss Sharing Arrangements (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Provision (benefit) for credit losses	$ (1,160)	$ 4,246	$ (1,983)	$ 9,669
Loss sharing agreements
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Expected reimbursement from loss sharing partners, beginning balance	2,005	2,653	2,159	2,166
Amounts due from partners which reduced net charge-offs	(128)	(293)	(269)	(595)
Provision (benefit) for credit losses	(166)	73	(179)	862
Expected reimbursement from loss sharing partners, ending balance	$ 1,711	$ 2,433	$ 1,711	$ 2,433