STOCKHOLDERS' EQUITY - Narrative (Details) - USD ($) $ / shares in Units, shares in Thousands						3 Months Ended		4 Months Ended	5 Months Ended	9 Months Ended
	May 05, 2021	May 04, 2021	Dec. 23, 2020	Dec. 26, 2019	Aug. 02, 2019	Sep. 30, 2021	Sep. 30, 2020	May 05, 2021	Dec. 26, 2019	Sep. 30, 2021	Sep. 30, 2020	Nov. 02, 2021	Feb. 18, 2021	Dec. 31, 2020	Dec. 22, 2020	Jul. 31, 2019	Jul. 30, 2019	Dec. 14, 2017
Equity, Class of Treasury Stock [Line Items]
Share repurchase authorization													$ 3,000,000,000				$ 3,000,000,000	$ 3,000,000,000
Remaining share repurchase authorization at replacement													$ 250,000,000				$ 1,030,000,000.00
Increase in treasury stock from stock repurchases						$ 3,000,000	$ 5,000,000			$ 36,000,000	$ 30,000,000
Common shares acquired in connection with employee stock plans (in shares)										90	80
Common shares acquired in connection with employee stock plans, amount										$ 36,000,000	$ 30,000,000
Noncontrolling interests						$ 22,000,000				$ 22,000,000				$ 0
July 2019 ASR
Equity, Class of Treasury Stock [Line Items]
Accelerated stock repurchase agreement amount																$ 1,000,000,000
Accelerated stock repurchase payment					$ 1,000,000,000
Shares received (in shares)				700	2,700				3,400
Increase in treasury stock from stock repurchases					$ 800,000,000
Decrease in capital in excess of par value					$ 200,000,000
Average daily volume weighted-average share price of common stock during term of agreement (in dollars per share)									$ 296.19
Reclassification from capital in excess of par value to treasury stock				$ 200,000,000
December 2020 ASR
Equity, Class of Treasury Stock [Line Items]
Accelerated stock repurchase agreement amount															$ 1,750,000,000
Accelerated stock repurchase payment			$ 1,750,000,000
Shares received (in shares)			3,800					4,400
Increase in treasury stock from stock repurchases			$ 1,500,000,000
Decrease in capital in excess of par value			262,500,000
Reclassification from capital in excess of par value to treasury stock	$ 262,500,000
December 2020 ASR | Citi
Equity, Class of Treasury Stock [Line Items]
Accelerated stock repurchase payment			$ 875,000,000
Shares received (in shares)		300	1,900
Average daily volume weighted-average share price of common stock during term of agreement (in dollars per share)		$ 400.07
December 2020 ASR | JPM
Equity, Class of Treasury Stock [Line Items]
Accelerated stock repurchase payment			$ 875,000,000
Shares received (in shares)	300		1,900
Average daily volume weighted-average share price of common stock during term of agreement (in dollars per share)	$ 401.49
Subsequent event
Equity, Class of Treasury Stock [Line Items]
Remaining authorized amount												$ 3,000,000,000