Contingencies - Additional Information (Details)	1 Months Ended			3 Months Ended	12 Months Ended
	Dec. 31, 2017 USD ($)	Jun. 30, 2015 USD ($)	Dec. 31, 2012 clinic	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Other Commitments [Line Items]
Loss contingency liability	$ 6,000,000				$ 6,000,000	$ 69,000,000
Gain on litigation settlement					$ 526,827,000	$ 0	$ (495,000,000)
Series of individually immaterial business acquisitions
Other Commitments [Line Items]
Number of vascular centers acquired | clinic			2
US Attorney Prescription Drug Investigation
Other Commitments [Line Items]
Litigation settlement amount awarded (paid)	(63,700,000)
U.S. Department of Veterans Affairs (VA)
Other Commitments [Line Items]
Litigation settlement amount awarded (paid)				$ (538,000,000)
Gain on litigation settlement				527,000,000
Vainer Private Civil Suit
Other Commitments [Line Items]
Litigation settlement amount awarded (paid)		$ 450,000,000
Legal fees		$ 45,000,000
Operating Income (Loss) | U.S. Department of Veterans Affairs (VA)
Other Commitments [Line Items]
Gain on litigation settlement				530,000,000
Noncontrolling Interest | U.S. Department of Veterans Affairs (VA)
Other Commitments [Line Items]
Gain on litigation settlement				9,000,000
Equity Method Investments | Noncontrolling Interest | U.S. Department of Veterans Affairs (VA)
Other Commitments [Line Items]
Gain on litigation settlement				$ 3,000,000
Incremental Cash Portion | US Attorney Prescription Drug Investigation
Other Commitments [Line Items]
Litigation settlement amount awarded (paid)	(41,500,000)
Cash Paid For Portion Previously Refunded | US Attorney Prescription Drug Investigation
Other Commitments [Line Items]
Litigation settlement amount awarded (paid)	$ (22,200,000)