Consolidated Investment Products (Investments Measured at NAV as a practical expedient) (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
Sep. 30, 2018	Dec. 31, 2017
Schedule of Investments [Line Items]
Real Estate Investments, Net	$ 12.1	$ 76.2
Private Equity Funds [Member]
Schedule of Investments [Line Items]
Investment Owned, at Fair Value	185.0	163.4
Unfunded Commitments	$ 83.0	$ 53.9
Weighted Average Remaining Term	5 years 6 months	5 years 6 months
Fair Value, Inputs, Level 3 [Member]
Schedule of Investments [Line Items]
Real Estate Investments, Net	$ 12.1	$ 76.2

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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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Value of the investment at close of period. For schedules of investments that are categorized, the value would be aggregated by category. For investment in and advances to affiliates, if operations of any controlled companies are different in character from those of the company, group such affiliates within divisions and by type of activities.

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Amount of real estate investments, net of accumulated depreciation, which may include the following: (1) land available-for-sale; (2) land available-for-development; (3) investments in building and building improvements; (4) tenant allowances; (5) developments in-process; (6) rental properties; (7) other real estate investments; (8) real estate joint ventures; and (9) unconsolidated real estate and other joint ventures not separately presented.

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