Condensed Consolidated Statements of Changes in Stockholders' Equity (Unaudited) - USD ($) $ in Millions	Total	Preferred Stock [Member]	Common Stock	Additional Paid-in Capital	Retained Earnings	Treasury Stock, Common	Treasury Stock, Common Share-based Payment Arrangement [Member]	AOCI Attributable to Parent [Member]
Beginning balance at Dec. 31, 2023				$ 648	$ 19,007	$ (1,816)		$ (2,849)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares under incentive and stock compensation plans and other				(194)
Stock-based compensation plans expense				110
Net income	$ 2,258				2,258
Dividends declared on preferred stock					(16)
Dividends declared on common stock					(415)
Treasury stock acquired	(1,100)					(1,111)
Issuance of shares under incentive and stock compensation plans from treasury stock and other							$ 288
Net shares acquired related to employee incentive and stock compensation plans						(83)
Total other comprehensive income (loss)								844
Ending balance at Sep. 30, 2024	$ 17,008	$ 334	$ 3	564	20,834	(2,722)		(2,005)
Preferred Stock, Shares Outstanding, Ending Balance at Sep. 30, 2024		13,800
Common Shares Outstanding, beginning of period at Dec. 31, 2023			298,472,000
Shares Granted or Issued, Share-based Payment Arrangement [Abstract]
Treasury stock acquired	(11,000,000)		(11,007,000)
Issuance of shares under incentive and stock compensation plans and other			4,216,000
Return of shares under incentive and stock compensation plans to treasury stock			(864,000)
Common Shares Outstanding, at end of period at Sep. 30, 2024			290,817,000
Shares Granted or Issued, Share-based Payment Arrangement [Abstract]
Cash dividends declared per common share	$ 1.410
Cash dividends declared per preferred share	$ 1,125
Beginning balance at Jun. 30, 2024				558	20,209	(2,356)		(3,068)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares under incentive and stock compensation plans and other				(18)
Stock-based compensation plans expense				24
Net income	$ 767				767
Dividends declared on preferred stock					(6)
Dividends declared on common stock					(136)
Treasury stock acquired						(404)
Issuance of shares under incentive and stock compensation plans from treasury stock and other							41
Net shares acquired related to employee incentive and stock compensation plans						(3)
Total other comprehensive income (loss)								1,063
Ending balance at Sep. 30, 2024	$ 17,008	$ 334	$ 3	564	20,834	(2,722)		(2,005)
Preferred Stock, Shares Outstanding, Ending Balance at Sep. 30, 2024		13,800
Common Shares Outstanding, beginning of period at Jun. 30, 2024			293,989,000
Shares Granted or Issued, Share-based Payment Arrangement [Abstract]
Treasury stock acquired			(3,660,000)
Issuance of shares under incentive and stock compensation plans and other			512,000
Return of shares under incentive and stock compensation plans to treasury stock			(24,000)
Common Shares Outstanding, at end of period at Sep. 30, 2024			290,817,000
Shares Granted or Issued, Share-based Payment Arrangement [Abstract]
Cash dividends declared per common share	$ 0.470
Cash dividends declared per preferred share	$ 375.00
Beginning balance at Dec. 31, 2024	$ 16,447			578	21,531	(3,113)		(2,886)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares under incentive and stock compensation plans and other				(161)
Stock-based compensation plans expense				116
Net income	2,705				2,705
Dividends declared on preferred stock					(16)
Dividends declared on common stock					(441)
Treasury stock acquired	(1,200)					(1,212)
Issuance of shares under incentive and stock compensation plans from treasury stock and other							200
Net shares acquired related to employee incentive and stock compensation plans						(71)
Total other comprehensive income (loss)								883
Ending balance at Sep. 30, 2025	$ 18,450	$ 334	$ 3	533	23,779	(4,196)		(2,003)
Preferred Stock, Shares Outstanding, Ending Balance at Sep. 30, 2025		13,800
Common Shares Outstanding, beginning of period at Dec. 31, 2024			287,556,000
Shares Granted or Issued, Share-based Payment Arrangement [Abstract]
Treasury stock acquired	(9,900,000)		(9,894,000)
Issuance of shares under incentive and stock compensation plans and other			2,596,000
Return of shares under incentive and stock compensation plans to treasury stock			(624,000)
Common Shares Outstanding, at end of period at Sep. 30, 2025			279,634,000
Shares Granted or Issued, Share-based Payment Arrangement [Abstract]
Cash dividends declared per common share	$ 1.560
Cash dividends declared per preferred share	$ 1,125
Beginning balance at Jun. 30, 2025				527	22,850	(3,812)		(2,384)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares under incentive and stock compensation plans and other				(12)
Stock-based compensation plans expense				18
Net income	$ 1,080				1,080
Dividends declared on preferred stock					(6)
Dividends declared on common stock					(145)
Treasury stock acquired						(404)
Issuance of shares under incentive and stock compensation plans from treasury stock and other							$ 22
Net shares acquired related to employee incentive and stock compensation plans						(2)
Total other comprehensive income (loss)								381
Ending balance at Sep. 30, 2025	$ 18,450	$ 334	$ 3	$ 533	$ 23,779	$ (4,196)		$ (2,003)
Preferred Stock, Shares Outstanding, Ending Balance at Sep. 30, 2025		13,800
Common Shares Outstanding, beginning of period at Jun. 30, 2025			282,275,000
Shares Granted or Issued, Share-based Payment Arrangement [Abstract]
Treasury stock acquired			(3,139,000)
Issuance of shares under incentive and stock compensation plans and other			512,000
Return of shares under incentive and stock compensation plans to treasury stock			(14,000)
Common Shares Outstanding, at end of period at Sep. 30, 2025			279,634,000
Shares Granted or Issued, Share-based Payment Arrangement [Abstract]
Cash dividends declared per common share	$ 0.520
Cash dividends declared per preferred share	$ 375.00

HARTFORD INSURANCE GROUP, INC. 10-Q