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Other Investments - Investments Measured at NAV as a Practical Expedient (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
NAV of investments at fair value
Unfunded Commitments	$ 187.2	$ 158.3
Life of funds (generally up to)	15 years
Private equity funds
NAV of investments at fair value
Unfunded Commitments	$ 187.2	158.3
investments in other strategies
NAV of investments at fair value
Unfunded Commitments	0.0	0.0
Fair Value Measured at NAV
NAV of investments at fair value
Fair Value	430.5	371.2
Fair Value Measured at NAV | Controlling Interest
NAV of investments at fair value
Fair Value	324.9	275.1
Fair Value Measured at NAV | Private equity funds
NAV of investments at fair value
Fair Value	424.4	356.4
Fair Value Measured at NAV | investments in other strategies
NAV of investments at fair value
Fair Value	$ 6.1	$ 14.8

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Fair value of investment other than investment in equity security, investment in debt security and equity method investment. Includes, but is not limited to, investment in certain entities that calculate net asset value per share. Example includes, but is not limited to, investment in hedge fund, venture capital fund, private equity fund, and real estate partnership or fund.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 35
-Paragraph 54B
-Publisher FASB
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The amount of unfunded commitments for which the entity is obligated, to those certain investments for which net asset value per share is calculated (including by unit, membership interest, or other equity (ownership interest) unit measure) (alternative investments).

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