INCOME TAXES - Components of Income Tax and Reconciliation and Deferred Taxes (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Components of income before income taxes:
Domestic									$ 591.9	$ 1,052.7	$ 883.8
Foreign									146.5	162.3	178.7
Income from continuing operations before income taxes	$ 167.4	$ 164.2	$ 193.8	$ 213.0	$ 363.8	$ 343.0	$ 263.1	$ 245.1	738.4	1,215.0	1,062.5
Deferred
Total deferred									(186.1)	16.3	(113.8)
Total provision for income taxes	37.0	42.6	51.4	34.8	110.7	54.3	39.3	65.2	165.8	$ 269.5	$ 293.3
Federal statutory rate (as a percent)										21.00%	35.00%
Reconciliation of recorded federal provision for income taxes to the expected amount computed by applying the federal statutory rate
Expected expense at statutory rate									155.1	$ 255.1	$ 371.9
Increase (decrease) in income taxes resulting from:
State income taxes, net of federal benefit									33.6	57.4	14.5
Foreign rate differential									(2.3)	11.6	(26.0)
Foreign restructuring										(48.0)
Impact of 2017 Tax Reform									(30.2)	(29.7)	(64.9)
Global intangible low-taxed income									8.7	15.5
Non-deductible expenses (non-taxable income)									9.1	3.7	(4.6)
Other									(8.2)	3.9	2.4
Total provision for income taxes	37.0	$ 42.6	$ 51.4	$ 34.8	110.7	$ 54.3	$ 39.3	$ 65.2	165.8	269.5	293.3
Deferred tax assets
Deferred revenue	9.5				10.6				9.5	10.6
Allowance for doubtful accounts	267.6				267.0				267.6	267.0
Net operating loss carryforwards and other carryforwards	69.0				57.8				69.0	57.8
Stock-based compensation and other employee benefits	13.7				24.4				13.7	24.4
Lease liabilities	74.4								74.4
Accrued expenses and other	40.3				66.2				40.3	66.2
Intangibles	23.2								23.2
Total deferred tax assets	497.7				426.0				497.7	426.0
Valuation allowance	(64.0)				(36.3)				(64.0)	(36.3)
Deferred tax assets, net of valuation allowance	433.7				389.7				433.7	389.7
Deferred tax liabilities
Deferred income	365.6				409.8				365.6	409.8
Depreciation	41.8				79.0				41.8	79.0
Right of use assets	61.1								61.1
Intangible assets					113.4					113.4
Total deferred tax liabilities	468.5				602.2				468.5	602.2
Total - Net deferred tax liability	(34.8)				(212.5)				(34.8)	(212.5)
Amounts recognized in the consolidated balance sheets:
Non-current assets	45.2				44.0				45.2	44.0
Non-current liabilities	(80.0)				(256.5)				(80.0)	(256.5)
Total - Net deferred tax liability	$ (34.8)				$ (212.5)				(34.8)	(212.5)
Continuing Operations
Components of income before income taxes:
Income from continuing operations before income taxes									738.4	1,215.0	1,062.5
Current
Federal									126.0	152.2	295.0
State									35.8	58.0	17.5
Foreign									11.5	52.8	56.7
Total current									173.3	263.0	369.2
Deferred
Federal									(11.8)	48.0	(65.3)
State									6.7	14.7	6.2
Foreign									(2.4)	(56.2)	(16.8)
Total deferred									(7.5)	6.5	(75.9)
Total provision for income taxes									165.8	269.5	293.3
Increase (decrease) in income taxes resulting from:
Total provision for income taxes									$ 165.8	$ 269.5	$ 293.3