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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
	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

X

- 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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X

- Definition

Adjustments to Additional Paid in Capital Decrease in Carrying Amount of Redeemable Noncontrolling Interests

+ References

No definition available.

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X

- Definition

Affiliate Equity [Abstract]

+ References

No definition available.

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X

- 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.

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X

- 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

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