CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement [Abstract]
Revenue	$ 4,204.1	$ 3,604.2	$ 3,484.5
Expenses
Operating	1,222.8	1,026.6	976.3
Selling, general and administrative	991.4	936.4	921.3
Restructuring		12.0
Depreciation and amortization	158.3	126.7	113.5
Litigation settlement		863.8
Acquisition-Related Expenses	22.5
Total expenses	2,395.0	2,965.5	2,011.1
Operating income	1,809.1	638.7	1,473.4
Non-operating (expense) income, net
Interest expense, net	(188.4)	(137.8)	(115.1)
Other non-operating income, net	(4.7)	57.1	21.3
Purchase price hedge gain	111.1
CCXI gains	59.7
Total non-operating income (expense), net	(22.3)	(80.7)	(93.8)
Income before provision for income taxes	1,786.8	558.0	1,379.6
Provision for income taxes	779.1	282.2	430.0
Net income	1,007.7	275.8	949.6
Less: Net income attributable to noncontrolling interests	7.1	9.2	8.3
Net income attributable to Moody's	$ 1,000.6	$ 266.6	$ 941.3
Earnings per share
Basic	$ 5.24	$ 1.38	$ 4.7
Diluted	$ 5.15	$ 1.36	$ 4.63
Weighted average shares outstanding
Basic	191.1	192.7	200.1
Diluted	194.2	195.4	203.4