CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 1,429	$ 1,320	$ 1,008
Foreign Currency Adjustments:
Foreign currency translation adjustment - Pre Tax	(22)	(315)	225
Foreign currency translation adjustment - Tax	(1)	0	0
Foreign currency translation adjustment - Net of Tax	(23)	(315)	225
Foreign currency translation adjustments - reclassification of losses included in net income - Pre Tax	32	0	0
Foreign currency translation adjustments - reclassification of losses included in net income - Tax	0	0	0
Foreign currency translation adjustments - reclassification of losses included in net income - Net of Tax	32	0	0
Net gains (losses) on net investment hedges - Pre Tax	35	41	(59)
Net gains (losses) on net investment hedges, Tax	(9)	(7)	23
Net gains (losses) on net investment hedges, Net of Tax	26	34	(36)
Net investment hedges - reclassification of gains included in net income - Pre Tax	(3)	0	0
Net investment hedges - reclassification of gains included in net income - Tax	1	0	0
Net investment hedges - reclassification of gains included in net income - Net of Tax	(2)	0	0
Cash Flow Hedges:
Net realized and unrealized gain (loss) on cash flow hedges - Pre Tax	0	(1)	10
Net realized and unrealized gain (loss) on cash flow hedges - Tax	0	0	(4)
Net realized and unrealized gain (loss) on cash flow hedges - Net of Tax	0	(1)	6
Reclassification of (losses) gains included in net income - Pre Tax	0	0	(12)
Reclassification of (losses) gains included in net income - Tax	0	0	5
Reclassification of (losses) gains included in net income - Net of Tax	0	0	(7)
Available for Sale Securities:
Net unrealized gains on available for sale securities - Pre Tax	0	0	2
Net unrealized gains on available for sale securities - Tax	0	0	0
Net unrealized gains on available for sale securities - Net of Tax	0	0	2
Reclassification of gains included in net income - Pre Tax	0	0	(4)
Reclassification of gains included in net income - Tax	0	0	0
Reclassification of gains included in net income - Net of Tax	0	0	(4)
Pension and Other Retirement Benefits:
Amortization of actuarial losses and prior service costs included in net income - Pre Tax	3	5	8
Amortization of actuarial losses and prior service costs included in net income - Tax	(1)	(1)	(3)
Amortization of actuarial losses and prior service costs included in net income - Net of Tax	2	4	5
Net actuarial (loss)/gain arising during the period	(32)	6	21
Net actuarial (losses) gains and prior service costs - Tax	8	(2)	(8)
Net actuarial (losses) gains and prior service costs - Net of Tax	(24)	4	13
Total other comprehensive (loss) income - Pre Tax	13	(264)	191
Total other comprehensive (loss)income - Tax	(2)	(10)	13
Total Other Comprehensive Income (Loss)	11	(274)	204
Comprehensive Income	1,440	1,046	1,212
Less: comprehensive income (loss) attributable to noncontrolling interests	11	(12)	19
Comprehensive Income Attributable to Moody’s	$ 1,429	$ 1,058	$ 1,193