Summary of Significant Accounting Policies and Implementation of New Financial Accounting Standards (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Mar. 11, 2019	Jan. 01, 2019	Dec. 31, 2017
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Advertising expense	$ 1,100.0	$ 1,100.0	$ 900.0
Advertising expense, percentage of revenue	5.00%	5.00%	5.00%
Operating lease, right-of-use asset					$ 530.0
Contract liabilities	$ 276.8	$ 264.6
Operating lease, liability	$ 663.7				$ 595.0
Operating Lease, Liability, Statement of Financial Position [Extensible List]	us-gaap:OtherLiabilitiesNoncurrent	us-gaap:OtherLiabilitiesNoncurrent			us-gaap:OtherLiabilitiesNoncurrent
Stockholders' equity	$ 5,825.2	$ 2,699.1
Deferred tax assets	730.5	385.1
Retained Earnings
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Stockholders' equity	7,830.2	4,920.4	$ 11,395.9			$ 13,894.1
Accumulated Other Comprehensive Loss
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Stockholders' equity	$ (6,496.4)	$ (6,523.6)	(5,729.2)			(5,718.6)
Tax Cuts and Jobs Act, reclassification from AOCI to retained earnings, tax effect			$ 105.2
Cumulative Effect, Period of Adoption, Adjustment | Retained Earnings
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Stockholders' equity						763.8
Cumulative Effect, Period of Adoption, Adjustment | Accumulated Other Comprehensive Loss
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Stockholders' equity						(105.2)
Discontinued Operations, Disposed of by Sale | Elanco | Eli Lilly and Company
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Disposition of ownership interest				80.20%
Accounting Standards Update 2016-02
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Contract liabilities					$ (65.0)
Accounting Standards Update 2014-09 | Cumulative Effect, Period of Adoption, Adjustment | Retained Earnings
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Stockholders' equity						5.0
Accounting Standards Update 2016-16 | Cumulative Effect, Period of Adoption, Adjustment
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Deferred tax assets						2,500.0
Deferred tax liabilities						1,800.0
Accounting Standards Update 2016-16 | Cumulative Effect, Period of Adoption, Adjustment | Retained Earnings
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Stockholders' equity						$ 700.0