CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Statement of Comprehensive Income [Abstract]
Net Income	$ 474	$ 467	$ 1,787	$ 1,463
Other Comprehensive Income (Loss):
Foreign currency translation adjustment - Pre Tax	(124)	204	(234)	107
Foreign currency translation adjustments - Tax	5	(17)	9	(11)
Foreign currency translation adjustments - Net of Tax	(119)	187	(225)	96
Net gains (losses) on net investment hedges - Pre Tax	99	(191)	233	(169)
Net gains (losses) on net investment hedges, Tax	(26)	48	(56)	42
Net gains (losses) on net investment hedges - Net of Tax	73	(143)	177	(127)
Net investment hedges - reclassification of gains included in net income - Pre Tax			(2)	0
Net investment hedges - reclassification of gains included in net income - Tax			1	0
Net investment hedges - reclassification of gains included in net income - Net of Tax			(1)	0
Cash Flow Hedges:
Net realized and unrealized (losses) gains on cash flow hedges - Pre Tax			0	(68)
Net realized and unrealized (losses) gains on cash flow hedges - Tax			0	18
Net realized and unrealized (losses) gains on cash flow hedges - Net of Tax			0	(50)
Reclassification of losses (gains) included in net income - Pre Tax	1	0	2	1
Reclassification of losses (gains) included in net income - Tax	0	0	0	0
Reclassification of losses (gains) included in net income - Net of Tax	1	0	2	1
Pension and Other Retirement Benefits:
Amortization of actuarial losses and prior service costs included in net income - Pre Tax	3	2	16	5
Amortization of actuarial losses and prior service costs included in net income - Tax	(1)	0	(4)	(1)
Amortization of actuarial losses and prior service costs included in net income - Net of Tax	2	2	12	4
Net actuarial (losses) gains and prior service costs - Pre Tax	4	(9)	4	(1)
Net actuarial (losses) gains and prior service costs - Tax	(1)	2	(1)	0
Net actuarial (losses) gains and prior service costs - Net of Tax	3	(7)	3	(1)
Total other comprehensive income (loss) - Pre Tax	(17)	6	19	(125)
Total other comprehensive income (loss) - Tax	(23)	33	(51)	48
Total other comprehensive income (loss) - Net of Tax	(40)	39	(32)	(77)
Comprehensive income	434	506	1,755	1,386
Less: comprehensive income (loss) attributable to noncontrolling interests	(3)	1	(2)	(12)
Comprehensive Income Attributable to Moody's	$ 437	$ 505	$ 1,757	$ 1,398