Securities Purchased Under Agreements to Resell and Securities Sold Under Agreements to Repurchase - Securities Sold under Agreements to Repurchase (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Investments, Debt and Equity Securities [Abstract]
Balance at December 31	$ 531.9	$ 39.8
Average Balance During the Year	$ 232.0	$ 218.3
Average Interest Rate Paid During the Year	0.07%	0.47%
Maximum Month-End Balance During the Year	$ 892.6	$ 269.8