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Other Investments - Investments Measured at NAV as a Practical Expedient (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
NAV of investments at fair value
Unfunded Commitments	$ 156.3	$ 122.2
Life of funds (generally up to)	15 years
Private equity funds
NAV of investments at fair value
Unfunded Commitments	$ 156.3	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	324.8	243.4
Fair Value Measured at NAV | Controlling Interest
NAV of investments at fair value
Fair Value	224.4	164.4
Fair Value Measured at NAV | Private equity funds
NAV of investments at fair value
Fair Value	310.2	235.4
Fair Value Measured at NAV | investments in other strategies
NAV of investments at fair value
Fair Value	$ 14.6	$ 8.0

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-Publisher FASB
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-Section 50
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