CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Statement of Comprehensive Income [Abstract]
Net Income	$ 577	$ 509	$ 1,313	$ 996
Other Comprehensive Income (Loss):
Foreign currency translation adjustment - Pre Tax	37	78	(110)	(97)
Foreign currency translation adjustments - Tax	(2)	1	4	6
Foreign currency translation adjustments - Net of Tax	35	79	(106)	(91)
Net gains (losses) on net investment hedges - Pre Tax	(41)	(97)	134	22
Net gains (losses) on net investment hedges, Tax	12	24	(30)	(6)
Net gains (losses) on net investment hedges, Net of Tax	(29)	(73)	104	16
Net investment hedges - reclassification of gains included in net income - Pre Tax	(1)	0	(2)	0
Net investment hedges - reclassification of gains included in net income - Tax	1	0	1	0
Net investment hedges - reclassification of gains included in net income - Net of Tax	0	0	(1)	0
Cash Flow Hedges:
Net realized and unrealized (losses) gains on cash flow hedges - Pre Tax	0	(20)	0	(68)
Net realized and unrealized (losses) gains on cash flow hedges - Tax	0	6	0	18
Net realized and unrealized (losses) gains on cash flow hedges - Net of Tax	0	(14)	0	(50)
Reclassification of losses (gains) included in net income - Pre Tax			1	1
Reclassification of losses (gains) included in net income - Tax			0	0
Reclassification of losses (gains) included in net income - Net of Tax			1	1
Pension and Other Retirement Benefits:
Amortization of actuarial losses and prior service costs included in net income - Pre Tax	10	1	13	3
Amortization of actuarial losses and prior service costs included in net income - Tax	(2)	0	(3)	(1)
Amortization of actuarial losses and prior service costs included in net income - Net of Tax	8	1	10	2
Net actuarial (losses) gains and prior service costs - Pre Tax	0	9	0	8
Net actuarial (losses) gains and prior service costs - Tax	0	(2)	0	(2)
Net actuarial (losses) gains and prior service costs - Net of Tax	0	7	0	6
Total other comprehensive income (loss) - Pre Tax	5	(29)	36	(131)
Total other comprehensive income (loss) - Tax	9	29	(28)	15
Total other comprehensive income (loss) - Net of Tax	14	0	8	(116)
Comprehensive income	591	509	1,321	880
Less: comprehensive income (loss) attributable to noncontrolling interests	(1)	(11)	1	(13)
Comprehensive Income Attributable to Moody's	$ 592	$ 520	$ 1,320	$ 893