Pledged and Restricted Assets - Accepted Collateral (Details) - USD ($)	Dec. 31, 2021	Dec. 31, 2020
Customer Securities for which Entity has Right to Sell or Repledge (Including Securities Sold or Repledged) [Line Items]
Total Collateral Accepted	$ 2,109,800,000	$ 1,680,700,000
Fair value of securities received as collateral that have been resold or repledged	1,419,000,000	0
Reverse repurchase agreements
Customer Securities for which Entity has Right to Sell or Repledge (Including Securities Sold or Repledged) [Line Items]
Collateral that may be repledged or sold	1,457,000,000	1,179,800,000
Collateral that may not be repledged or sold	650,000,000.0	500,000,000.0
Derivative contracts
Customer Securities for which Entity has Right to Sell or Repledge (Including Securities Sold or Repledged) [Line Items]
Collateral that may be repledged or sold	$ 2,800,000	$ 900,000