NEW ACCOUNTING PRONOUNCEMENTS - Revenue and Restricted Cash Standards Impact on Cash Flows (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016
OPERATING ACTIVITIES
Net income including noncontrolling interest	$ 248.2	$ 257.3	$ 1,518.6	$ 1,246.5
Adjustments to reconcile net income to cash provided by operating activities:
Deferred income taxes	13.3	3.3
Increase (Decrease) in Operating Capital [Abstract]
Accounts receivable	33.9	76.4
Other liabilities	(18.0)	(74.2)
Cash provided by operating activities	487.2	425.7
INVESTING ACTIVITIES
Cash used for investing activities	(255.8)	(995.3)
Effect of exchange rate changes on cash, cash equivalents and restricted cash	(2.3)	5.8
Decrease in cash, cash equivalents and restricted cash	(35.9)	(168.3)
Cash, cash equivalents and restricted cash, beginning of period	211.4	380.4	380.4
Cash, cash equivalents and restricted cash, end of period	$ 175.5	212.1	211.4	380.4
Previously Reported
OPERATING ACTIVITIES
Net income including noncontrolling interest		256.8
Adjustments to reconcile net income to cash provided by operating activities:
Deferred income taxes		3.2
Increase (Decrease) in Operating Capital [Abstract]
Accounts receivable		76.3
Other liabilities		(73.5)
Cash provided by operating activities		425.7
INVESTING ACTIVITIES
Restricted cash activity		53.8
Cash used for investing activities		(941.5)
Effect of exchange rate changes on cash, cash equivalents and restricted cash		5.0
Decrease in cash, cash equivalents and restricted cash		(115.3)
Cash, cash equivalents and restricted cash, beginning of period		327.4	327.4
Cash, cash equivalents and restricted cash, end of period		212.1		327.4
Adjustment | Restricted Cash Standard Adoption
INVESTING ACTIVITIES
Restricted cash activity		(53.8)
Cash used for investing activities		(53.8)
Effect of exchange rate changes on cash, cash equivalents and restricted cash		0.8
Decrease in cash, cash equivalents and restricted cash		(53.0)
Cash, cash equivalents and restricted cash, beginning of period		53.0	$ 53.0
Cash, cash equivalents and restricted cash, end of period				$ 53.0
Adjustment | Revenue Standard Adoption
OPERATING ACTIVITIES
Net income including noncontrolling interest		0.5
Adjustments to reconcile net income to cash provided by operating activities:
Deferred income taxes		0.1
Increase (Decrease) in Operating Capital [Abstract]
Accounts receivable		0.1
Other liabilities		$ (0.7)