BASIS OF FINANCIAL STATEMENT PRESENTATION (Details) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2018 USD ($) $ / shares	Mar. 31, 2017 USD ($) $ / shares	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Contract with Customer, Liability	$ 412.3		$ 377.4
Amortization of Deferred Sales Commissions	4.2	$ 3.7
Assets, Current	2,896.6		2,733.8
Assets, Noncurrent			13,939.2
Net Cash Provided by (Used in) Operating Activities	$ 154.7	$ 225.9
Percent of Revenue Contributed	100.00%	100.00%
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	$ 13.2
Revenues	2,848.3	$ 2,413.7
Cost of Revenue	2,069.3	1,701.2
Gross Profit	779.0	712.5
Selling, general and administrative expenses	397.0	342.9
Nonoperating Income (Expense)	(63.9)	(52.8)
Other Nonoperating Income		104.3
Provision for income taxes	69.0	82.0
Net earnings	172.5	183.3
Less: Net earnings attributable to the noncontrolling interest	0.7	(0.3)
Net Income (Loss) Attributable to Parent	$ 173.2	$ 183.0
Basic earnings per common share (in dollars per share) | $ / shares	$ 1.70	$ 1.79
Diluted earnings per common share (in dollars per share) | $ / shares	$ 1.67	$ 1.75
Net Cash Provided by (Used in) Investing Activities	$ (74.3)	$ (245.5)
Net Cash Provided by (Used in) Financing Activities	(40.0)	(51.9)
Effect of exchange rate changes on cash and cash equivalents	4.7	3.4
Cash and Cash Equivalents, Period Increase (Decrease)	45.1	(68.1)
Assets	16,831.7		16,673.0
Liabilities, Current	2,104.0		2,185.7
Liabilities, Noncurrent			7,662.4
Common stock, 92.8 and 93.5 shares outstanding at March 31, 2013 and December 31, 2012, respectively	20.2		20.8
Stockholders' Equity Attributable to Parent	6,984.0	5,653.2	6,804.1	$ 5,518.2
Liabilities and Equity	16,831.7		16,673.0
Capitalized Contract Cost, Amortization	0.6	0.1
Deferred Revenue, Revenue Recognized	71.0	55.1
Revenue, Remaining Performance Obligation	3,900.0
Contract with Customer, Performance Obligation Satisfied in Previous Period	$ 22.1
Ownership percentage below which investments are generally accounted for on the cost method (in thousandths)	20.00%
LabCorp Diagnostics [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Revenue, Net		$ 1,639.7
Percent of Revenue Contributed	62.10%	67.90%
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification		$ 78.2
Revenues	$ 1,770.2
Covance Drug Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Revenue, Net		$ 774.2
Percent of Revenue Contributed	37.90%	32.10%
Revenues	$ 1,078.5
Investigator fees [Member] | Covance Drug Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	57.4
Measure of progress [Member] | Covance Drug Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	12.5
sales commissions [Member] | Covance Drug Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	$ 1.4
Previous Accounting Guidance [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net cash provided by (used in) operating activities, as reported		$ 233.8
Current assets, as reported			2,682.6
Gross profit, as reported		803.6
Noncurrent assets, as reported			13,885.4
Total assets, as reported			16,568.0
Net Cash Provided by (Used in) Investing Activities, as reported		(245.5)
Revenues		2,447.0
Cost of Revenue		1,643.4
Selling, general and administrative expenses		419.4
Nonoperating Income (Expense)		104.5
Provision for income taxes		87.2
Net income (loss), including portion attributable to NCI, as reported		192.5
Less: Net earnings attributable to the noncontrolling interest		(0.3)
Net income (loss) attributable to Parent, as reported		$ 192.2
Basic earnings per common share (in dollars per share) | $ / shares		$ 1.87
Diluted earnings per common share (in dollars per share) | $ / shares		$ 1.84
Net Cash Provided by (Used in) Financing Activities, as reported		$ (59.8)
Effect of Exchange Rate on Cash and Cash Equivalents, as reported		3.4
Cash and Cash Equivalents, Period Increase (Decrease)		(68.1)
Current liabilities, as reported			2,046.1
Noncurrent liabilities, as reported			7,671.1
Noncontrolling Interest Mezzanine Equity, as reported			20.8
Shareholders Equity Attributable to Parent, as reported			6,830.0
Total liabilities and shareholders equity, as reported			$ 16,568.0
Other Current Assets [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
ASU 606 adjustment to previously reported amounts		51.2
Other Noncurrent Assets [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
ASU 606 adjustment to previously reported amounts		53.8
Assets [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
ASU 606 adjustment to previously reported amounts		105.0
Other Current Liabilities [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
ASU 606 adjustment to previously reported amounts		139.6
Other Noncurrent Liabilities [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
ASU 606 adjustment to previously reported amounts		(8.7)
Noncontrolling Interest [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
ASU 606 adjustment to previously reported amounts		0.0
Shareholders' Equity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
ASU 606 adjustment to previously reported amounts		(25.9)
Total liabilities and shareholder's equity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
ASU 606 adjustment to previously reported amounts		105.0
Revenue from Contract with Customer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
ASU 606 adjustment to previously reported amounts		(33.3)
ASU 715 pension adjustment to previously reported amounts		0.0
Gross profit [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
ASU 606 adjustment to previously reported amounts		(91.1)
ASU 715 pension adjustment to previously reported amounts		0.0
Selling, General and Administrative Expenses [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
ASU 606 adjustment to previously reported amounts		(76.8)
ASU 715 pension adjustment to previously reported amounts		0.3
Nonoperating Income (Expense) [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
ASU 606 adjustment to previously reported amounts		0.1
ASU 715 pension adjustment to previously reported amounts		(0.3)
Provision for income taxes [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
ASU 606 adjustment to previously reported amounts		(5.2)
ASU 715 pension adjustment to previously reported amounts		0.0
Net earnings [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
ASU 606 adjustment to previously reported amounts		(9.2)
ASU 715 pension adjustment to previously reported amounts		0.0
Net earnings attributable to NCI [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
ASU 606 adjustment to previously reported amounts		0.0
ASU 715 pension adjustment to previously reported amounts		0.0
Cost of Sales [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
ASU 606 adjustment to previously reported amounts		57.8
ASU 715 pension adjustment to previously reported amounts		0.0
Net earnings attributable to company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
ASU 606 adjustment to previously reported amounts		(9.2)
ASU 715 pension adjustment to previously reported amounts		0.0
Net cash from operating activities [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
ASU 606 adjustment to previously reported amounts		$ 0.0
ASC 230 Cash flow presentation adjustment		(7,900,000)
Net cash from investing activities [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
ASU 606 adjustment to previously reported amounts		$ 0.0
Net Cash Provided by (Used in) Investing Activities		0.0
Net cash from financing activities [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
ASU 606 adjustment to previously reported amounts		0.0
Net Cash Provided by (Used in) Financing Activities		7.9
Effect of exchange rate on cash and cash equivalents [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
ASU 606 adjustment to previously reported amounts		0.0
Effect of exchange rate changes on cash and cash equivalents		$ 0.0