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Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Dec. 31, 2025	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Income Tax Examination [Line Items]
Effective tax rate (percent)		25.40%	24.00%	24.20%	23.50%
Excess tax benefits from stock compensation				$ 30
Unrecognized tax benefits, period increase (decrease), net of federal tax benefits		$ 5		19
Unrecognized tax benefits, period increase (decrease)				$ 21
Income tax examination, description				Moody’s is subject to U.S. federal income tax as well as income tax in various state, local and foreign jurisdictions. The Company's U.S. federal income tax returns for 2021 through 2024 remain open to examination. The Company’s New York City tax returns for 2018 through 2022 are currently under examination, and 2023 is open to examination. The Company's U.K. corporate income tax returns are currently under audit for years 2017 through 2021, while years 2022 through 2023 remain open to examination.
Forecast
Income Tax Examination [Line Items]
Unrecognized tax benefits, reduction resulting from lapse of applicable statute of limitations	$ 64
Unrecognized tax benefits, reduction resulting from lapse of applicable statute of limitations, related interest	$ 15

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Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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