Redeemable Noncontrolling Interest (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Beginning Balance	$ 304.3
Issuance of Redeemable Noncontrolling Interest at January 1, 2018			$ 732.4
Total Other Comprehensive Income, Net of Tax	8.9	$ 0.8	(2.8)
Redeemable Noncontrolling Interest Redemption Value Adjustment	12.2	(30.2)	(19.4)
Reclassification to Redeemable Noncontrolling Interest for Share Repurchases	(210.9)	12.5	12.5
Ending Balance	0.0	304.3
Redeemable Noncontrolling Interest
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Beginning Balance	304.3	275.8
Net Income (Loss) Attributable to Redeemable Noncontrolling Interest	(3.2)	16.3
Total Other Comprehensive Income, Net of Tax	8.9	0.8
Redeemable Noncontrolling Interest Redemption Value Adjustment	12.2	30.2
Reclassification to Redeemable Noncontrolling Interest for Share Repurchases	(296.1)	(12.5)
Distributions of Membership Interest	(1.7)	(6.3)
Ending Balance	$ 0.0	$ 304.3	$ 275.8

Other Comprehensive Income (Loss), Net Of Tax, Portion Attributable To Redeemable Noncontrolling Interest

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- Definition

Temporary Equity, Distributions Of Membership Interest

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- Definition

Change in noncontrolling interest during the period as a result of a change in the redemption value of redeemable noncontrolling interest.

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Decrease in noncontrolling interest (for example, but not limited to, redeeming or purchasing the interests of noncontrolling shareholders, issuance of shares (interests) by the non-wholly owned subsidiary to the parent entity for other than cash, and a buyback of shares (interest) by the non-wholly owned subsidiary from the noncontrolling interests).

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount of increase in noncontrolling interest from a business combination.

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- Definition

As of the reporting date, the aggregate carrying amount of all noncontrolling interests which are redeemable by the (parent) entity (1) at a fixed or determinable price on a fixed or determinable date, (2) at the option of the holder of the noncontrolling interest, or (3) upon occurrence of an event that is not solely within the control of the (parent) entity. This item includes noncontrolling interest holder's ownership (or holders' ownership) regardless of the type of equity interest (common, preferred, other) including all potential organizational (legal) forms of the investee entity.

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- Definition

The portion of net income or loss attributable to temporary equity interest.

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