Income Taxes - Narrative (Details) $ in Millions, ₩ in Billions	3 Months Ended	12 Months Ended
	Jun. 30, 2021 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2021 KRW (₩)	Dec. 31, 2021 USD ($)	Dec. 31, 2020 KRW (₩)	Dec. 31, 2020 USD ($)	Dec. 31, 2017	Feb. 29, 2012 KRW (₩)	Feb. 29, 2012 USD ($)
Tax Credit Carryforward [Line Items]
Income taxes paid		$ 72.7
Deferred tax liabilities, temporary differences, purchase accounting, foreign subsidiaries						$ 1,500.0
Total deferred charges and prepaid taxes						39.6		$ 142.2
Deferred tax asset, net	$ 490.0
Deferred tax asset, gross	945.0
Increase in unrecognized tax benefit	$ 455.0
Valuation allowance						1,961.3		1,753.9
Unrecognized tax benefit				$ 122.7		87.5		68.8
Net interest expense		2.7	$ 1.0	$ 4.7
Unrecognized tax benefits, interest on income taxes accrued						24.8		21.2
Decrease in unrecognized tax benefits is reasonably possible						475.0
Samsung Bioepis
Tax Credit Carryforward [Line Items]
Investment in Samsung Bioepis					₩ 713.3	599.9	₩ 673.8	620.2		₩ 49.5	$ 45.0
2017 Tax Act
Tax Credit Carryforward [Line Items]
Transition toll tax liabilities						633.0		697.0
Foreign Tax Authority
Tax Credit Carryforward [Line Items]
Increase in unrecognized tax benefit		455.0
General Business | Domestic Country
Tax Credit Carryforward [Line Items]
Operating loss carryforwards						0.6
Tax credit carryforward, amount						4.8
Operating loss carryforward, subject to expiration						16,700.0
General Business | Foreign Tax Authority
Tax Credit Carryforward [Line Items]
Operating loss carryforward, subject to expiration						16,200.0
Research | State and Local Jurisdiction
Tax Credit Carryforward [Line Items]
Tax credit carryforward, amount						147.6
Earnings in the form of cash and cash equivalents | 2017 Tax Act
Tax Credit Carryforward [Line Items]
Transition toll tax repatriation tax rate									15.50%
Other Foreign Earnings | 2017 Tax Act
Tax Credit Carryforward [Line Items]
Transition toll tax repatriation tax rate									8.00%
Minimum
Tax Credit Carryforward [Line Items]
Residual U.S. tax liability on reversal of deferred tax liabilities on foreign subsidiaries purchase accounting						300.0
Maximum
Tax Credit Carryforward [Line Items]
Residual U.S. tax liability on reversal of deferred tax liabilities on foreign subsidiaries purchase accounting						400.0
TECFIDERA
Tax Credit Carryforward [Line Items]
Deferred tax assets, value, reduction in value								1,700.0
Deferred tax liabilities, value, reduction in value								$ 1,600.0
Income tax expense, reduction in deferred tax assets and liabilities, net			$ 90.3
Deferred tax assets, increase in value		108.5
Deferred tax liability, increase in value		$ 103.9
ADUHELM
Tax Credit Carryforward [Line Items]
Valuation allowance						$ 390.0