Income Taxes (Narrative) (Details) - USD ($) $ in Millions		1 Months Ended	3 Months Ended		12 Months Ended
		Jan. 26, 2018	Dec. 31, 2017	Dec. 31, 2016	Sep. 30, 2018
Income Tax Disclosure [Line Items]
U.S. federal statutory tax rate (percent)			35.00%
Net expense in consolidated income statements related to change in tax law			$ 239.0
Expense related to repatriation tax and future repatriation effect on foreign investments			453.0
Expense related to repatriation tax and future repatriation effect on foreign investments impacting income tax provision			420.5
Change In tax rate, deferred tax liability, income tax (expense) benefit			214.0
Component of tax-related adjustment payable over eight years			364.1
Component of tax-related adjustment resulting from withholding taxes and other impacts			56.4
Foreign tax credits expected to offset repatriation tax			53.8
Tax liabilities not expected to be offset by foreign tax credits			310.3
Transition tax for accumulated foreign earnings, liability, noncurrent			$ 296.6
Effective tax rate (percent)			64.20%
Income tax payments, net of refunds			$ 61.0	$ 96.7
Forecast
Income Tax Disclosure [Line Items]
U.S. federal statutory tax rate (percent)					24.50%
Subsequent Event
Income Tax Disclosure [Line Items]
U.S. federal statutory tax rate (percent)		21.00%
Segment Reconciling Items
Income Tax Disclosure [Line Items]
Impact of new tax law on equity affiliate expense	[1]		$ 32.5	$ 0.0

[1] (A) For additional information on the impact of the U.S. Tax Cuts and Jobs Act, including our equity affiliate impact, refer to Note 17, Income Taxes.