Investments (Narratives) (Details) - USD ($) $ in Millions	12 Months Ended
Mar. 31, 2023	Mar. 31, 2022	Mar. 31, 2021
Investments, Debt and Equity Securities [Abstract]
Assets held by insurance regulators	$ 23.4	$ 27.1
Fair value of sold available-for-sale securities	196.2	352.3	$ 523.9
Available for sale securities, realized gain	0.9	9.5	9.6
Available for sale securities, realized loss	0.3	$ 1.4	$ 2.1
Other-than-temporary impairments	2.0
Available for sale investments, unrealized loss position
Available for sale investments, fair value, recovery amount	$ 0.5
Mortgages [Member] \| Minimum [Member]
Real Estate [Abstract]
Mortgage loan interest rate	3.50%
Mortgages [Member] \| Maximum [Member]
Real Estate [Abstract]
Mortgage loan interest rate	6.50%

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Interest rate of mortgage loan within investment in mortgage loan on real estate by entity with substantial portion of business acquiring and holding investment real estate or interest in real estate.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 12
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-Subsection 29

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale in a continuous loss position, recovered amount at fair value.

+ References

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Carrying amount of cash and investment securities on deposit with state regulatory authorities in connection with capital requirements.

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-Publisher FASB
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-SubTopic 825
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Amount of realized gain on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of realized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount, before tax, of other-than-temporary impairment (OTTI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), recognized in other comprehensive income (OCI).

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Amount of cash inflow from sale of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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