STOCKHOLDERS' EQUITY - Narrative (Details) - USD ($)												1 Months Ended			3 Months Ended	4 Months Ended	12 Months Ended
	Dec. 16, 2022	Dec. 16, 2022	Dec. 15, 2022	Nov. 02, 2022	Mar. 30, 2022	Mar. 30, 2022	Mar. 29, 2022	Jan. 12, 2022	May 05, 2021	May 04, 2021	Dec. 23, 2020	Feb. 15, 2024	Oct. 31, 2023	Dec. 16, 2022	Mar. 30, 2022	May 05, 2021	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Feb. 16, 2024	Feb. 15, 2023	Nov. 04, 2022	Nov. 03, 2022	Jan. 11, 2022	Feb. 18, 2021	Dec. 22, 2020	Jul. 30, 2019
Equity, Class of Treasury Stock [Line Items]
Cash dividend declared (in dollars per share)													$ 0.885
Dividends													$ 108,000,000
Share repurchase authorization																									$ 3,000,000,000		$ 3,000,000,000
Shares received (in shares)																		0	0
Increase in treasury stock from share repurchases																	$ 1,586,000,000	$ 2,096,000,000	$ 79,000,000
Remaining authorized amount																									$ 1,000,000,000
Common shares acquired in connection with employee stock plans (in shares)																	200,000	200,000	200,000
Common shares acquired in connection with employee stock plans, amount																	$ 73,000,000	$ 96,000,000	$ 79,000,000
Aggregate statutory capital and surplus in our state regulated insurance subsidiaries																	12,200,000,000	11,300,000,000
Aggregate minimum regulatory requirements of statutory capital and surplus																	9,800,000,000	8,400,000,000
Ordinary dividends that may be paid to parent company																	1,100,000,000
Actual dividends paid to parent company																	$ 1,800,000,000	$ 1,300,000,000	$ 1,600,000,000
Subsequent Event
Equity, Class of Treasury Stock [Line Items]
Cash dividend declared (in dollars per share)												$ 0.885
2021 Share Repurchase Authorization
Equity, Class of Treasury Stock [Line Items]
Share repurchase authorization																					$ 3,000,000,000
Remaining authorized amount																					1,000,000,000
2023 Share Repurchase Authorization
Equity, Class of Treasury Stock [Line Items]
Share repurchase authorization																					$ 3,000,000,000
Shares received (in shares)																	3,100,000
Increase in treasury stock from share repurchases																	$ 1,500,000,000
Stock repurchase average price (in dollars per share)																	$ 482.27
2023 Share Repurchase Authorization | Forecast
Equity, Class of Treasury Stock [Line Items]
Remaining authorized amount																				$ 824,000,000
2024 Share Repurchase Authorization | Forecast
Equity, Class of Treasury Stock [Line Items]
Share repurchase authorization																				$ 3,000,000,000
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)											3,800,000					4,400,000
Increase in treasury stock from share 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 share repurchase payment											$ 875,000,000
Shares received (in shares)										300,000	1,900,000
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 share repurchase payment											$ 875,000,000
Shares received (in shares)									300,000		1,900,000
Average daily volume weighted-average share price of common stock during term of agreement (in dollars per share)									$ 401.49
January 2022 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)								2,200,000							2,400,000
Increase in treasury stock from share repurchases								$ 850,000,000
Decrease in capital in excess of par value								150,000,000
Reclassification from capital in excess of par value to treasury stock						$ 150,000,000
January 2022 ASR | Mizuho Markets Americas LLC
Equity, Class of Treasury Stock [Line Items]
Accelerated share repurchase payment								$ 500,000,000
Shares received (in shares)							100,000	1,080,000.00
Average daily volume weighted-average share price of common stock during term of agreement (in dollars per share)							$ 410.96
January 2022 ASR | Wells Fargo Bank
Equity, Class of Treasury Stock [Line Items]
Accelerated share repurchase payment								$ 500,000,000
Shares received (in shares)					100,000			1,080,000.00
Average daily volume weighted-average share price of common stock during term of agreement (in dollars per share)					$ 411.66
November 2022 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)				1,500,000										1,800,000
Increase in treasury stock from share repurchases				$ 850,000,000
Decrease in capital in excess of par value				$ 150,000,000
Reclassification from capital in excess of par value to treasury stock		$ 150,000,000
November 2022 ASR | Mizuho Markets Americas LLC
Equity, Class of Treasury Stock [Line Items]
Accelerated share repurchase payment																						$ 500,000,000
Shares received (in shares)	177,000			760,000
Average daily volume weighted-average share price of common stock during term of agreement (in dollars per share)	$ 533.87
November 2022 ASR | Goldman Sachs
Equity, Class of Treasury Stock [Line Items]
Accelerated share repurchase payment																							$ 500,000,000
Shares received (in shares)			177,000	760,000
Average daily volume weighted-average share price of common stock during term of agreement (in dollars per share)			$ 534.16