CONSOLIDATED STATEMENT OF SHAREHOLDERS' EQUITY (UNAUDITED) (Parenthetical) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Statement of Stockholders' Equity [Abstract]
Dividends declared per share attributable to Moody's common shareholders (in USD per share)	$ 0.56	$ 0.50	$ 1.68	$ 1.50
Currency translation adjustment, net of net investment hedge activity, tax expense (benefit)	$ 31	$ (34)	$ (31)	$ (33)
Net actuarial gains and prior service cost, tax expense (benefit)	(2)	0	0	(1)
Amortization of prior service costs and actuarial losses, tax expense	$ 0	$ 0	1	$ 1
Net realized and unrealized gain on cash flow hedges, tax expense (benefit)			$ (18)