Other Assets and Other Liabilities - Components of Other Liabilities (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Other Assets And Other Liabilities [Abstract]
Lease liabilities	$ 313.2
Future contingent commitments for affordable housing investments	141.1	$ 119.7
Accrued expenses payable	104.3	87.9
Fair value of derivative financial instruments (notes 20 and 22)	96.2	139.0
Liabilities for supplemental retirement plans	84.4	86.6
Accrued employee benefits	74.8	66.6
Accrued interest payable	21.7	25.4
Loan payments in process	18.8	51.2
Other postretirement plans	18.7	15.3
Payables arising from securities brokerage and insurance businesses	9.6	29.7
Other	22.7	73.8
Total other liabilities	$ 905.5	$ 695.2