Income Taxes (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Contingency [Line Items]
Current Foreign Tax Expense (Benefit)			$ 158.2	$ 74.7	$ 107.5
Effective Income Tax Rate Reconciliation, Tax Credit, Foreign, Amount			$ 196.1	$ 54.2	$ 33.2
Effective Income Tax Rate Reconciliation, Tax Credit, Foreign, Percent			0.10%	1.60%	3.90%
Foreign Earnings Repatriated			$ 187.6	$ 206.1	$ 171.7
Repatriation of foreign earnings, amount			$ 269.5	$ 108.7	$ 35.4
Foreign-derived intangible income			12.40%	44.80%	6.50%
Deferred Income Tax Expense (Benefit)			$ (455.5)	$ 32.9	$ (45.9)
Income tax expense			$ 225.5	(164.6)	(104.5)
Effective Income Tax Rate Reconciliation, Deduction, Percent			0.80%
Income Tax Benefit, Foreign-Derived Intangible Income			$ 17.0
Tax Cuts and Jobs Act of 2017, income tax benefit, foreign tax credits				$ 67.7	171.1
Tax Cuts And Jobs Act Of 2017, Incomplete Accounting, Change In Tax Rate, Provisional Income Tax Benefit, Foreign, Percent				28.00%
Tax Cuts and Jobs Act of 2017, transition tax, Income expense					177.9
Tax Cut and Jobs Act of 2017, global intangible low-taxed income minimum tax, income tax expense					$ 165.4
Effective Income Tax Rate Reconciliation, Tax Cuts And Jobs Act Of 2017, Change In Income Tax Rate, Percent					62.70%
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Share-based Compensation Cost, Amount				$ 21.1
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Share-based Compensation Cost, Percent				8.70%
Tax Cuts and Jobs Act of 2017, Transition tax, Income expense, percent					32.50%
Decrease effective tax rate					3.60%
Effective income tax rate reconciliation, Tax Cuts and Jobs Act of 2017, amount				$ (56.5)	$ 45.8
Effective income tax rate reconciliation, Tax Cuts and Jobs Act of 2017, percent					0.084
Tax Cuts and Jobs Act of 2017, transition tax, foreign income subject to domestic taxation					$ 195.6
Tax Cuts and Jobs Act of 2017, transition tax, foreign tax credit					17.7
Tax Cuts and Jobs Act of 2017, deferred tax asset, income tax expense, amount					$ 292.4
Other permanent differences			0.00%	0.00%	53.40%
Tax Cuts and Jobs Act of 2017, income tax expense, amount, foreign income subject to domestic taxation					$ 121.3
Tax Cuts and Jobs Act of 2017, income tax expense, amount, foreign income subject to domestic taxation, percent					(22.20%)
Tax Cuts and Jobs Act of 2017, income tax benefit, foreign tax credits, percent					(31.20%)
Tax Cuts and Jobs Act of 2017, deferred tax liability, income tax benefit					$ (5.1)
Tax Cuts And Jobs Act Of 2017, Incomplete Accounting, Change In Tax Rate, Provisional Income Tax Expense (Benefit), Permanent Differences, Percentage					0.90%
Effective Income Tax Rate Reconciliation, Tax Cut And Jobs Act 2017, Global Intangible Low-Taxed Income Minimum Tax, Percent					30.20%
Tax Cut and Jobs Act of 2017, global intangible low-taxed income minimum tax, income tax expense, deferred tax expense				$ 67.7	$ 236.9
Tax Cut and Jobs Act of 2017, global intangible low-taxed income minimum tax, income tax benefit, unrecognized tax benefit					71.5
Tax Cuts and Jobs Act of 2017, transition tax, estimated tax credits					28.0
Tax Cuts and Jobs Act of 2017, estimated deferred tax liabilities, foreign				11.1	533.4
Effective Income Tax Rate Reconciliation, Tax Cuts and Jobs Act of 2017, Transition Tax on Accumulated Foreign Earnings, Amount			$ (1,408.2)
Change in unrecognized tax benefits			$ 4.6	35.4	27.1
Statute of limitations, minimum (years)			3 years
Statute of limitations, maximum (years)			6 years
Federal [Member]
Income Tax Contingency [Line Items]
Net operating loss carryforwards	$ 12.5		$ 12.5
Income tax credit carryforwards	280.5		280.5
State and Local Jurisdiction [Member]
Income Tax Contingency [Line Items]
Current Foreign Tax Expense (Benefit)			193.2	58.1	54.4
Tax Cuts and Jobs Act of 2017, deferred tax asset, income tax expense, amount					2.9
Tax Cuts and Jobs Act of 2017, deferred tax liability, estimated increase in income tax payable					2.2
Tax Cuts and Jobs Act of 2017, deferred tax asset, estimated increase in deferred taxes					$ 0.7
Net operating loss carryforwards	43.7		43.7
Income tax credit carryforwards	67.3		67.3
Tax credit carryforwards, subject to expiration	47.2		47.2
Tax credit carryforwards, not subject to expiration	20.1		20.1
In Process Research and Development [Member] | Wilson Therapeutics And Syntimmune [Member]
Income Tax Contingency [Line Items]
Income tax expense				$ (248.4)
In Process Research and Development [Member] | Wilson Therapeutics [Member]
Income Tax Contingency [Line Items]
Effective Income Tax Rate Reconciliation, Other Reconciling Items, Amount				69.70%
In Process Research and Development [Member] | Syntimmune, Inc [Member]
Income Tax Contingency [Line Items]
Effective Income Tax Rate Reconciliation, Other Reconciling Items, Amount				32.90%
Intellectual Property Election [Member] | Wilson Therapeutics [Member]
Income Tax Contingency [Line Items]
Deferred Income Tax Expense (Benefit)		$ (95.7)	(95.7)
Valuation Allowance Release [Member]
Income Tax Contingency [Line Items]
Deferred Income Tax Expense (Benefit)		$ (30.3)	(30.3)
Wilson Therapeutics [Member]
Income Tax Contingency [Line Items]
Income tax expense			(10.2)
Subsidiaries [Member]
Income Tax Contingency [Line Items]
Effective Income Tax Rate Reconciliation, Tax Credit, Foreign, Amount	$ 1,839.3
Effective Income Tax Rate Reconciliation, Tax Credit, Foreign, Percent	17.50%
Subsidiaries [Member] | Intellectual Property Election [Member]
Income Tax Contingency [Line Items]
Deferred Income Tax Expense (Benefit)	$ (2,221.5)
Connecticut | State and Local Jurisdiction [Member]
Income Tax Contingency [Line Items]
Net operating loss carryforwards	27.3		27.3
Income tax credit carryforwards	$ 39.7		$ 39.7