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Affiliate Equity - Effect of Changes in the Company's Ownership Interest in its Affiliates on the Controlling Interest's Equity (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
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Dec. 31, 2018 | [1] | Sep. 30, 2018 | [1] | Jun. 30, 2018 | Mar. 31, 2018 | Dec. 31, 2017 | [2] | Sep. 30, 2017 | Jun. 30, 2017 | Mar. 31, 2017 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Affiliate Equity [Abstract] |  |  |  |  |  |  |  |  |  |  |
Net income (controlling interest) | $ (151.3) | $ 124.9 | $ 117.0 | $ 153.0 | $ 315.4 | $ 125.4 | $ 126.3 | $ 122.5 | $ 243.6 | $ 689.5 | $ 472.8
Increase (decrease) in controlling interest paid-in capital from Affiliate equity issuances |  |  |  |  |  |  |  |  | (5.0) | (1.0) | 1.6
Decrease in controlling interest paid-in capital from Affiliate equity repurchases |  |  |  |  |  |  |  |  | (67.9) | (116.2) | (38.0)
Net income (controlling interest) including the net impact of Affiliate equity transactions |  |  |  |  |  |  |  |  | $ 170.7 | $ 572.3 | $ 436.4
[1] | For the year ended December 31, 2018, the Company recorded expenses to reduce the carrying value of the U.S. alternative Affiliate to zero and one of its non-U.S. alternative Affiliates accounted for under the equity method to fair value (see Note 13 for additional information).
[2] | In the fourth quarter of 2017, the Company recorded a one-time net benefit from changes in U.S. tax laws (see Note 22 for additional information) and an expense to reduce the carrying value of one of its U.S. alternative Affiliates accounted for under the equity method (see Note 13 for additional information).

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- Definition Adjustments to Additional Paid in Capital Decrease in Carrying Amount of Redeemable Noncontrolling Interests + References No definition available. + Details
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