Income Taxes - Additional Information (Details) - USD ($)		1 Months Ended	3 Months Ended			12 Months Ended
	Sep. 30, 2020	Sep. 30, 2018	Sep. 30, 2020	Mar. 31, 2020	Dec. 31, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Operating Loss Carryforwards [Line Items]
Income tax benefit					$ 37,000,000.0	$ 1,894,273,000	$ (112,971,000)	$ 438,469,000
CARES Act, tax benefit						720,600,000
Net current income tax receivable	$ 488,428,000		$ 488,428,000			488,428,000	5,859,000
Gross deferred tax asset	2,219,370,000		2,219,370,000			2,219,370,000	487,320,000
Valuation allowance for deferred tax assets	411,648,000		411,648,000			411,648,000	199,682,000
Legal accrual						6,722,346,000	185,145,000	61,527,000
Deferred tax benefit						1,544,971,000	(28,537,000)	795,524,000
Reserve for an uncertain tax position	478,351,000	$ 98,124,000	478,351,000			478,351,000	105,657,000	98,124,000	$ 323,869,000
Tax Cuts and Jobs Act, recognized income tax benefits					$ 37,000,000.0			612,600,000
Tax Cuts and Jobs Act, deferred income tax benefit as result of applying a lower U.S. federal income tax rate								897,600,000
Tax Cuts and Jobs Act, current income tax expense on historical foreign earnings and profits								285,000,000.0
Tax Cuts and Jobs Act, decrease in provisional transition tax						182,600,000
Adjustments recorded to deferred income taxes related to 2017 Tax Act						0
Undistributed earnings of international subsidiaries	3,000,000,000		3,000,000,000			3,000,000,000
Permanently reinvested cumulative undistributed earnings	2,300,000,000		2,300,000,000			2,300,000,000
Valuation allowance - increase (decrease)						(212,000,000.0)	(300,000)
Excess tax benefit from the exercise of stock options and lapses of restricted stock units						3,900,000	7,900,000	22,700,000
Income tax payments, net of refunds						139,400,000	117,700,000	104,000,000.0
Unrecognized tax benefits, including interest and penalties	498,300,000		498,300,000			498,300,000	124,200,000
Unrecognized tax benefits, including interest and penalties, net of federal benefit	455,500,000		455,500,000			455,500,000	95,000,000.0
Unrecognized tax benefits that would impact effective tax rate	437,200,000		437,200,000			437,200,000	76,800,000
Unrecognized tax benefits, interest and penalties	19,900,000		19,900,000			19,900,000	18,600,000
Reductions of tax positions of the prior years						(6,480,000)	(10,317,000)	(224,878,000)
Unrecognized tax benefits						385,797,000	$ 18,819,000	$ 2,804,000
Reduction of unrecognized tax benefits reasonably possible	13,900,000		13,900,000			$ 13,900,000
Swiss Federal Tax Administration
Operating Loss Carryforwards [Line Items]
Reduced tax rate for a period (in years)						10 years
Gross deferred tax asset	582,400,000		582,400,000			$ 582,400,000
Valuation allowance for deferred tax assets	221,700,000		221,700,000			221,700,000
Net deferred tax asset	360,700,000		360,700,000			360,700,000
PharMEDium Healthcare Holdings, Inc
Operating Loss Carryforwards [Line Items]
Ordinary tax deduction	2,400,000,000		2,400,000,000			2,400,000,000
Income tax benefit				$ (741,000,000.0)		655,000,000
Net current income tax receivable	488,400,000		488,400,000			488,400,000
Federal
Operating Loss Carryforwards [Line Items]
Potential tax benefits from net operating loss carryforwards	$ 12,400,000		12,400,000			12,400,000
Federal | Minimum
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards, term (in years)	1 year
Federal | Maximum
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards, term (in years)	17 years
State
Operating Loss Carryforwards [Line Items]
Potential tax benefits from net operating loss carryforwards	$ 201,200,000		201,200,000			201,200,000
Tax credit carryforwards	12,800,000		12,800,000			12,800,000
Foreign
Operating Loss Carryforwards [Line Items]
Potential tax benefits from net operating loss carryforwards	58,900,000		58,900,000			58,900,000
Foreign | Alternative minimum tax credit carryforwards
Operating Loss Carryforwards [Line Items]
Tax credit carryforwards	2,100,000		2,100,000			2,100,000
USAO - EDNY Civil Claims
Operating Loss Carryforwards [Line Items]
Litigation settlement, payment		$ 625,000,000.0
Opioid Lawsuits and Investigations
Operating Loss Carryforwards [Line Items]
Income tax benefit			1,100,000,000
Legal accrual			$ 6,600,000,000
Legal settlement term (in years)			18 years
Deferred tax benefit						1,100,000,000
Reserve for an uncertain tax position	$ 359,500,000		$ 359,500,000			359,500,000
Unrecognized tax benefits						$ 371,500,000