CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Statement of Comprehensive Income [Abstract]
Net Income	$ 509	$ 311	$ 996	$ 685
Foreign Currency Adjustments:
Foreign currency translation adjustment - Pre Tax	78	42	(97)	15
Foreign currency translation adjustments - Tax	1	0	6	0
Foreign currency translation adjustments - Net of Tax	79	42	(91)	15
Net gains on net investment hedges - Pre Tax	(97)	(36)	22	(6)
Net gains on net investment hedges, Tax	24	7	(6)	1
Net gains on net investment hedges, Net of Tax	(73)	(29)	16	(5)
Cash Flow Hedges:
Net realized and unrealized (losses) gains on cash flow hedges - Pre Tax	(20)	0	(68)	0
Net realized and unrealized (losses) gains on cash flow hedges - Tax	6	0	18	0
Net realized and unrealized (losses) gains on cash flow hedges - Net of Tax	(14)	0	(50)	0
Reclassification of losses (gains) included in net income - Pre Tax			1	0
Reclassification of losses (gains) included in net income - Tax			0	0
Reclassification of losses (gains) included in net income - Net of Tax			1	0
Pension and Other Retirement Benefits:
Amortization of actuarial losses and prior service costs included in net income - Pre Tax	1	1	3	2
Amortization of actuarial losses and prior service costs included in net income - Tax	0	0	(1)	(1)
Amortization of actuarial losses and prior service costs included in net income - Net of Tax	1	1	2	1
Net actuarial (losses) gains and prior service costs - Pre Tax	9	(3)	8	(2)
Net actuarial (losses) gains and prior service costs - Tax	(2)	1	(2)	1
Net actuarial (losses) gains and prior service costs - Net of Tax	7	(2)	6	(1)
Total other comprehensive income (loss) - Pre Tax	(29)	4	(131)	9
Total other comprehensive income (loss) - Tax	29	8	15	1
Total other comprehensive income (loss) - Net of Tax	0	12	(116)	10
Comprehensive income	509	323	880	695
Less: comprehensive (loss) income attributable to noncontrolling interests	(11)	4	(13)	12
Comprehensive Income Attributable to Moody's	$ 520	$ 319	$ 893	$ 683