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Investment Securities - Debt securities issued by corporation (Details) - Debt securities issued by corporations - USD ($) $ in Millions	Mar. 31, 2023	Dec. 31, 2022
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	$ 1,010.4	$ 1,018.8
AAA
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	11.4	11.3
AA
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	95.9	96.0
A
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	558.8	567.9
BBB
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	338.0	337.7
Other
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	$ 6.3	$ 5.9

X

- Definition

Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=126976982&loc=d3e19207-110258

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+ References

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