Variable Interest Entities - Re-securitizations (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Transfers of securities to VIEs
U.S. GSEs and government agencies	$ 13,105	$ 2,717
U.S. GSEs and government agencies \| Nonconsolidated re-securitization VIEs
Variable Interest Entity [Line Items]
Interest in VIEs	$ 2,530		$ 2,631

Amount of net assets (liabilities).

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