Reserves for Expected Costs of Liquidation and Residual Wind-Down Claims and Costs - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Restructuring Cost and Reserve [Line Items]
Expected liquidation end date			Mar. 31, 2021
Legal Fees Reimbursement [Member]
Restructuring Cost and Reserve [Line Items]
Loss contingency Inestimable loss		$ 10.0		$ 10.0
Reserve for Expected Wind-Down Costs [Member]
Restructuring Cost and Reserve [Line Items]
Net increase (decrease in) additions to reserves for Expected Costs of Liquidation	$ 2.1	23.6	$ 4.7	20.7
Reserve for Expected Reporting Costs [Member]
Restructuring Cost and Reserve [Line Items]
Net increase (decrease in) additions to reserves for Expected Costs of Liquidation	$ 1.7	$ 7.9	$ 1.7	$ 6.8