Pledged and Restricted Assets (Accepted Collateral) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Mar. 31, 2022
Financial Instruments Owned and Pledged as Collateral [Line Items]
Total Collateral Accepted	$ 2,109,800,000	$ 2,689,600,000
Fair value of securities received as collateral that have been resold or repledged		1,663,000,000
Securities received as collateral, amount repledged and sold	1,419,000,000
Reverse repurchase agreements
Financial Instruments Owned and Pledged as Collateral [Line Items]
Collateral that may be repledged or sold	1,457,000,000	1,888,900,000
Reverse repurchase agreements	650,000,000.0	800,000,000.0
Derivative contracts
Financial Instruments Owned and Pledged as Collateral [Line Items]
Collateral that may be repledged or sold	$ 2,800,000	$ 700,000