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Affiliate Equity - Changes in the Company's Interest in its Affiliates on the Controlling Interest's Equity (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
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Jun. 30, 2018 | Jun. 30, 2017 | Jun. 30, 2018 | Jun. 30, 2017
Affiliate Equity [Abstract] |  |  |  |
Net income (controlling interest) | $ 117.0 | $ 126.3 | $ 270.0 | $ 248.8
Increase / (decrease) in controlling interest paid-in capital from Affiliate equity issuances | (2.3) | 0.9 | (3.3) | (0.3)
Increase / (decrease) in controlling interest paid-in capital from Affiliate equity repurchases | 1.0 | (16.5) | (32.1) | (69.1)
Net income (controlling interest) including net impact of Affiliate equity transactions | $ 115.7 | $ 110.7 | $ 234.6 | $ 179.4

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- Definition The increase (decrease) in additional paid-in capital of the reporting entity from purchases and sales of Affiliate equity. + References No definition available. + Details
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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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- Definition Affiliate Equity [Abstract] + References No definition available. + Details
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- Definition Increase (decrease) in equity during the period due to net income attributable to the parent company and net transfers with non-controlling interests. + References No definition available. + Details
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- Definition The portion of profit or loss for the period, net of income taxes, which is attributable to the parent. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-04(22)) -URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04(18)) -URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03(20)) -URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688 + Details
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