Deposits - (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Deposit Liability [Line Items]
Money market investments	$ 10,500.0	$ 6,600.0
Bank overdrafts	1.6	1.3
Carrying value of securities pledged as collateral	2,200.0	31.3
Time deposits equal to or grater than $250,000	224.0	$ 59.1
Century Bancorp, Inc.
Deposit Liability [Line Items]
Carrying value of securities pledged as collateral	$ 2,100.0

Carrying value as of the balance sheet date of payments made in excess of existing cash balances, which will be honored by the bank but reflected as a loan to the entity. Overdrafts generally have a very short time frame for correction or repayment and are therefore more similar to short-term bank financing than trade financing.

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Amount of securities, mortgage loans, or other financial instruments pledged as collateral for deposits.

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Amount of interest-bearing domestic money market demand account deposit liabilities.

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Amount of time deposit liabilities, including certificates of deposit, in denominations that meet or exceed the Federal Deposit Insurance Corporation (FDIC) insurance limit.

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