Cash and Cash Equivalents - Summary of Cash and Cash Equivalents (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Cash and Cash Equivalents [Abstract]
Cash and due from banks	$ 1,185	$ 723
Interest bearing deposits with the Federal Reserve Bank	12,406	13,700
Interest bearing deposits with other institutions	5,106	3,025
Securities purchased under agreements to resell	216	227
Other short-term investment securities	27	0
Total cash and cash equivalents	$ 18,940	$ 17,675