Comprehensive Income (Changes in AOCI) (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2018	Dec. 31, 2017
Changes in AOCI by component (net of tax) [Roll Forward]
Beginning balance	$ (157.4)	$ (195.1)	$ (157.4)	$ (195.1)
Other comprehensive loss before reclassifications			(61.6)	41.9
Amounts reclassified from AOCL			30.2	(4.2)
Net other comprehensive (loss) income			(31.4)	37.7
Ending balance	(188.8)		(188.8)	(157.4)
Gains (Losses) on Cash Flow Hedges [Member]
Changes in AOCI by component (net of tax) [Roll Forward]
Beginning balance	7.4	5.6	7.4	5.6
Other comprehensive loss before reclassifications			(8.9)	10.5
Amounts reclassified from AOCL			(4.7)	(8.7)
Net other comprehensive (loss) income			(13.6)	1.8
Ending balance	(6.2)			7.4
Unrealized Gains (Losses) on Available-for-Sale Securities [Member]
Changes in AOCI by component (net of tax) [Roll Forward]
Beginning balance	1.8	2.3	1.8	2.3
Other comprehensive loss before reclassifications			(1.8)	(0.5)
Amounts reclassified from AOCL			0.0	0.0
Net other comprehensive (loss) income			(1.8)	(0.5)
Ending balance	0.0			1.8
Defined Benefit Plan Items [Member]
Changes in AOCI by component (net of tax) [Roll Forward]
Beginning balance	(127.5)	(130.0)	(127.5)	(130.0)
Other comprehensive loss before reclassifications			(34.0)	(2.0)
Amounts reclassified from AOCL			7.0	4.5
Net other comprehensive (loss) income			(27.0)	2.5
Ending balance	(154.5)			(127.5)
Foreign Currency Translation Adjustments [Member]
Changes in AOCI by component (net of tax) [Roll Forward]
Beginning balance	(39.1)	(73.0)	(39.1)	(73.0)
Other comprehensive loss before reclassifications			(16.9)	33.9
Amounts reclassified from AOCL	27.9	$ 0.0	27.9	0.0
Net other comprehensive (loss) income			$ 11.0	33.9
Ending balance	$ (28.1)			$ (39.1)

Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Roll Forward]

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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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Amount after tax, before reclassification adjustments of other comprehensive income (loss).

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Amount after tax and reclassification adjustments of other comprehensive income (loss).

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