Cash and Cash Equivalents - Summary of Cash and Cash Equivalents (Footnote Information) (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Cash and Cash Equivalents [Abstract]
Deposits at the Federal Reserve Bank earning interest at the Federal Funds target rate	$ 16,600,000,000	$ 13,700,000,000
Interest-earning deposits in other financial institutions	3,400,000,000	3,000,000,000.0
Fair value of securities purchased under agreements to resell	294,500,000	232,200,000
Securities received as collateral, amount repledged and sold	$ 0	$ 0