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Other Investments - Investments Measured at NAV as a Practical Expedient (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
NAV of investments at fair value
Unfunded Commitments	$ 114.1	$ 122.2
Life of funds (generally up to)	15 years
Private equity funds
NAV of investments at fair value
Unfunded Commitments	$ 114.1	122.2
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	323.6	243.4
Fair Value Measured at NAV | Controlling Interest
NAV of investments at fair value
Fair Value	217.7	164.4
Fair Value Measured at NAV | Private equity funds
NAV of investments at fair value
Fair Value	307.0	235.4
Fair Value Measured at NAV | Investments in other strategies
NAV of investments at fair value
Fair Value	$ 16.6	$ 8.0

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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

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
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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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