CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Income Statement [Abstract]
Revenues	$ 1,175.1	$ 1,000.5	$ 2,301.8	$ 1,975.7
Expenses
Operating	320.2	284.8	635.1	560.1
Selling, general and administrative	270.5	216.1	541.6	436.8
Depreciation and amortization	48.4	32.9	97.5	65.4
Acquisition-Related Expenses	2.0	6.6	2.8	6.6
Total expenses	641.1	540.4	1,277.0	1,068.9
Operating Income	534.0	460.1	1,024.8	906.8
Non-operating (expense) income, net
Interest expense, net	(53.4)	(49.7)	(104.1)	(97.1)
Other non-operating income, net	14.9	10.4	15.9	2.7
Purchase price hedge gain		41.2		41.2
CCXI gains				59.7
Total non-operating (expense) income, net	(38.5)	1.9	(88.2)	6.5
Income before provisions for income taxes	495.5	462.0	936.6	913.3
Provision for income taxes	117.6	148.4	181.9	253.8
Net income	377.9	313.6	754.7	659.5
Less: Net income attributable to noncontrolling interests	1.7	1.4	5.6	1.7
Net income attributable to Moody's	$ 376.2	$ 312.2	$ 749.1	$ 657.8
Earnings per share attributable to Moody's common shareholders
Basic	$ 1.96	$ 1.63	$ 3.91	$ 3.44
Diluted	$ 1.94	$ 1.61	$ 3.85	$ 3.39
Weighted average number of shares outstanding
Basic	191.9	191.0	191.6	191.1
Diluted	194.4	193.8	194.5	194.1
Dividends declared per share attributable to Moody's common shareholders	$ 0.44	$ 0.38	$ 0.88	$ 0.38