Income Taxes (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Contingency [Line Items]
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Impairment Losses, Amount	$ 72.0	$ 608.0
Federal rate	21.00%	35.00%	35.00%
Adjustment of deferred tax balances			$ 36.0
Domestic production activities deduction			12.0
Federal research and development credits			6.0
Deferred Tax Assets, Valuation Allowance	$ 497.0	$ 407.0
Effect of expiration of statute of limitations during next twelve months	0.0
Gross tax liability for tax positions that may not be sustained under a more likely than not threshold	11.0
Accrued interest on tax liability	0.0	1.0
Deferred Tax Assets, Net, Current	1.5
Noncurrent deferred tax assets, net		1.5
Proceeds from Income Tax Refunds		51.0
Income tax benefit	5.0	$ 1.0	$ (45.0)
Income taxes paid	4.0
Tax deductible goodwill	1,952.0
Research Tax Credit Carryforward [Member]
Income Tax Contingency [Line Items]
Tax Credit Carryforward, Amount	19.0
State and Local Jurisdiction [Member]
Income Tax Contingency [Line Items]
Tax Credit Carryforward, Amount	35.0
Operating loss carryforward	9,400.0
Internal Revenue Service (IRS) [Member]
Income Tax Contingency [Line Items]
Operating loss carryforward	2,400.0
Impact Of Adoption Of ACS 606 [Member] | Accounting Standards Update 2014-09 [Member]
Income Tax Contingency [Line Items]
Income tax benefit	$ 7.0