Comprehensive Income And Accumulated Other Comprehensive Loss - Reclassification out of AOCI (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Derivative Instruments, Gain (Loss) [Line Items]
Other non-operating income, net	$ 6	$ 16
Provision for income taxes	(111)	(126)
Net income attributable to Moody's	498	736
Reclassification out of Accumulated Other Comprehensive Income
Derivative Instruments, Gain (Loss) [Line Items]
Net income attributable to Moody's	(1)	(2)
Losses on cash flow hedges | Reclassification out of Accumulated Other Comprehensive Income
Derivative Instruments, Gain (Loss) [Line Items]
Provision for income taxes	0	0
Net income attributable to Moody's	(1)	(1)
Losses on cash flow hedges | Reclassification out of Accumulated Other Comprehensive Income | Interest rate contract
Derivative Instruments, Gain (Loss) [Line Items]
Other non-operating income, net	(1)	(1)
Net Investment Hedges | Reclassification out of Accumulated Other Comprehensive Income
Derivative Instruments, Gain (Loss) [Line Items]
Provision for income taxes	0	0
Net income attributable to Moody's	0	1
Net Investment Hedges | Reclassification out of Accumulated Other Comprehensive Income | FX forwards
Derivative Instruments, Gain (Loss) [Line Items]
Other non-operating income, net	0	1
Total pension and other retirement benefits | Reclassification out of Accumulated Other Comprehensive Income
Derivative Instruments, Gain (Loss) [Line Items]
Provision for income taxes	0	1
Net income attributable to Moody's	0	(2)
Amortization of actuarial losses and prior service costs included in net income | Reclassification out of Accumulated Other Comprehensive Income
Derivative Instruments, Gain (Loss) [Line Items]
Other non-operating income, net	$ 0	$ (3)