STOCKHOLDERS' EQUITY - Narrative (Details) - USD ($) $ / shares in Units, shares in Thousands									1 Months Ended		3 Months Ended		5 Months Ended	12 Months Ended
	Jan. 29, 2021	Dec. 23, 2020	Dec. 26, 2019	Aug. 02, 2019	Feb. 28, 2019	Nov. 29, 2018	Mar. 26, 2018	Dec. 22, 2017	Feb. 18, 2021	Nov. 30, 2020	Feb. 28, 2019	Mar. 26, 2018	Dec. 26, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 22, 2020	Jul. 31, 2019	Jul. 30, 2019	Nov. 28, 2018	Dec. 21, 2017	Dec. 14, 2017
Equity, Class of Treasury Stock [Line Items]
Cash dividend declared (in dollars per share)										$ 0.625
Share repurchase authorization																			$ 3,000,000,000	$ 3,000,000,000.0	$ 3,000,000,000.0	$ 3,000,000,000
Increase in treasury stock from share repurchases														$ 1,820,000,000	$ 1,070,000,000	$ 1,090,000,000
Remaining share repurchase authorization at replacement																			$ 1,030,000,000.00
Common shares acquired in connection with employee stock plans (in shares)														200	200	400
Common shares acquired in connection with employee stock plans, amount														$ 70,000,000	$ 70,000,000	$ 116,000,000
Aggregate statutory capital and surplus in our state regulated insurance subsidiaries														9,400,000,000	8,000,000,000.0
Aggregate minimum regulatory requirements of statutory capital and surplus														7,000,000,000.0	5,900,000,000
Ordinary dividends that may be paid to parent company														1,400,000,000
Actual dividends paid to parent company														$ 1,300,000,000	$ 1,800,000,000	$ 2,300,000,000
December 2017 ASR
Equity, Class of Treasury Stock [Line Items]
Accelerated share repurchase agreement amount																					$ 1,000,000,000.0
Accelerated share repurchase payment								$ 1,000,000,000.0
Shares received (in shares)							460	3,280				3,740
Increase in treasury stock from share 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)												$ 267.55
Reclassification from capital in excess of par value to treasury stock							$ 200,000,000
November 2018 ASR
Equity, Class of Treasury Stock [Line Items]
Accelerated share repurchase agreement amount																				$ 750,000,000
Accelerated share repurchase payment						$ 750,000,000
Shares received (in shares)					600	1,940					2,540
Increase in treasury stock from share repurchases						$ 600,000,000
Decrease in capital in excess of par value						$ 150,000,000
Average daily volume weighted-average share price of common stock during term of agreement (in dollars per share)											$ 295.15
Reclassification from capital in excess of par value to treasury stock					$ 150,000,000
July 2019 ASR
Equity, Class of Treasury Stock [Line Items]
Accelerated share repurchase agreement amount																		$ 1,000,000,000
Accelerated share repurchase payment				$ 1,000,000,000
Shares received (in shares)			700	2,700									3,400
Increase in treasury stock from share 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 share repurchase agreement amount																	$ 1,750,000,000
Accelerated share repurchase payment		$ 1,750,000,000
Shares received (in shares)		3,800
Increase in treasury stock from share repurchases		$ 1,500,000,000
Decrease in capital in excess of par value		262,500,000
December 2020 ASR | Citi
Equity, Class of Treasury Stock [Line Items]
Accelerated share repurchase payment		$ 875,000,000
Shares received (in shares)		1,900
December 2020 ASR | JPM
Equity, Class of Treasury Stock [Line Items]
Accelerated share repurchase payment		$ 875,000,000
Shares received (in shares)		1,900
Subsequent Event
Equity, Class of Treasury Stock [Line Items]
Cash dividend declared (in dollars per share)									$ 0.70
Dividends paid	$ 81,000,000
Share repurchase authorization									$ 3,000,000,000
Remaining share repurchase authorization at replacement									$ 250,000,000