Equity - Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	6 Months Ended
Jun. 30, 2018	Dec. 31, 2017
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance beginning of period	$ 1,577.5
Unrealized (losses) gains, arising during the period	(11.5)
Amounts reclassified out of AOCI during the period, gross	14.4
Amounts reclassified out of AOCI during the period, taxes	(1.3)
Noncontrolling interest	(6.0)
Deferred taxes on unrealized gains (losses), arising during the period	(5.2)
Balance end of period	1,449.7
Accumulated other comprehensive loss	(436.7)	$ (427.1)
Accumulated Other Comprehensive Income Loss [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance beginning of period	(68.7)
Balance end of period	(78.3)
Foreign Currency Translation [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance beginning of period	(46.6)
Unrealized (losses) gains, arising during the period	(39.6)
Amounts reclassified out of AOCI during the period, gross	22.5
Amounts reclassified out of AOCI during the period, taxes	(4.2)
Noncontrolling interest	(6.0)
Deferred taxes on unrealized gains (losses), arising during the period	0.7
Balance end of period	(73.2)
Currency Derivative Contracts [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance beginning of period	(22.2)
Unrealized (losses) gains, arising during the period	28.1
Amounts reclassified out of AOCI during the period, gross	(7.9)
Amounts reclassified out of AOCI during the period, taxes	2.8
Noncontrolling interest	0.0
Deferred taxes on unrealized gains (losses), arising during the period	(5.9)
Balance end of period	(5.1)
Marketable Securities [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance beginning of period	0.1
Unrealized (losses) gains, arising during the period	0.0
Amounts reclassified out of AOCI during the period, gross	(0.2)
Amounts reclassified out of AOCI during the period, taxes	0.1
Noncontrolling interest	0.0
Deferred taxes on unrealized gains (losses), arising during the period	0.0
Balance end of period	0.0
AOCI Attributable to Noncontrolling Interest [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Accumulated other comprehensive loss	$ 358.4

Accumulated change in equity from transactions and other events and circumstances from non-owner sources, net of tax effect, at period end. Excludes Net Income (Loss), and accumulated changes in equity from transactions resulting from investments by owners and distributions to owners. Includes foreign currency translation items, certain pension adjustments, unrealized gains and losses on certain investments in debt and equity securities, other than temporary impairment (OTTI) losses related to factors other than credit losses on available-for-sale and held-to-maturity debt securities that an entity does not intend to sell and it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis, as well as changes in the fair value of derivatives related to the effective portion of a designated cash flow hedge.

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