Investments - Credit Loss Allowance on Investments (Details) - USD ($) $ in Millions	Dec. 31, 2020	Mar. 31, 2020
Investments, Debt and Equity Securities [Abstract]
Agent loans, allowance for credit loss	$ 1.1
Available-for-sales securities, allowance for credit loss	$ 0.2	$ 0.6

Amount of allowance for credit loss on financing receivable. Excludes allowance for financing receivable covered under loss sharing agreement.

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Name:	us-gaap_FinancingReceivableAllowanceForCreditLosses
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant