CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Statement of Comprehensive Income [Abstract]
Net Income	$ 467	$ 383	$ 1,463	$ 1,067
Foreign Currency Adjustments:
Foreign currency translation adjustment - Pre Tax	204	(194)	107	(179)
Foreign currency translation adjustments - Tax	(17)	0	(11)	0
Foreign currency translation adjustments - Net of Tax	187	(194)	96	(179)
Net gains (losses) on net investment hedges - Pre Tax	(191)	136	(169)	130
Net gains (losses) on net investment hedges, Tax	48	(34)	42	(33)
Net gains (losses) on net investment hedges, Net of Tax	(143)	102	(127)	97
Net investment hedges - reclassification of gains included in net income - Pre Tax	0	(1)	0	(1)
Net investment hedges - reclassification of gains included in net income - Tax	0	0	0	0
Net investment hedges - reclassification of gains included in net income - Net of Tax	0	(1)	0	(1)
Cash Flow Hedges:
Net realized and unrealized (losses) gains on cash flow hedges - Pre Tax			(68)	0
Net realized and unrealized (losses) gains on cash flow hedges - Tax			18	0
Net realized and unrealized (losses) gains on cash flow hedges - Net of Tax			(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	2	1	5	3
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	2	1	4	2
Net actuarial (losses) gains and prior service costs - Pre Tax	(9)	0	(1)	(2)
Net actuarial (losses) gains and prior service costs - Tax	2	0	0	1
Net actuarial (losses) gains and prior service costs - Net of Tax	(7)	0	(1)	(1)
Total other comprehensive income (loss) - Pre Tax	6	(58)	(125)	(49)
Total other comprehensive income (loss) - Tax	33	(34)	48	(33)
Total other comprehensive income (loss) - Net of Tax	39	(92)	(77)	(82)
Comprehensive income	506	291	1,386	985
Less: comprehensive income attributable to noncontrolling interests	1	3	(12)	15
Comprehensive Income Attributable to Moody's	$ 505	$ 288	$ 1,398	$ 970