Pledged and Restricted Assets - Narrative (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2021
Financial Instruments Owned and Pledged as Collateral [Line Items]
Amount of securities and loans pledged	$ 47,500.0	$ 54,600.0
Financial instruments owned and pledged as collateral, amount eligible to be repledged by counterparty	33.5	524.1
Average deposits maintained to meet Federal Reserve Bank reserve requirements	400.0
Collateral Requirements
Financial Instruments Owned and Pledged as Collateral [Line Items]
Amount of securities and loans pledged	$ 5,700.0	$ 5,600.0