Segment Information - Revenues (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Segment Reporting Information [Line Items]
Earned premiums and fee income	$ 4,670	$ 4,724	$ 13,913	$ 13,470
Net investment income	492	490	1,290	1,448
Net realized capital gains (losses)	6	89	(116)	332
Other revenues	3	44	108	129
Total revenues	5,171	5,347	15,195	15,379
Corporate
Segment Reporting Information [Line Items]
Earned premiums and fee income	13	18	47	43
Commercial Lines
Segment Reporting Information [Line Items]
Earned premiums and fee income	2,259	2,258	6,694	6,040
Commercial Lines | Workers’ compensation
Segment Reporting Information [Line Items]
Earned premiums and fee income	776	825	2,312	2,480
Commercial Lines | Liability
Segment Reporting Information [Line Items]
Earned premiums and fee income	355	330	1,035	731
Commercial Lines | Marine
Segment Reporting Information [Line Items]
Earned premiums and fee income	59	59	191	86
Commercial Lines | Package business
Segment Reporting Information [Line Items]
Earned premiums and fee income	390	376	1,150	1,092
Commercial Lines | Property
Segment Reporting Information [Line Items]
Earned premiums and fee income	200	198	590	529
Commercial Lines | Professional liability
Segment Reporting Information [Line Items]
Earned premiums and fee income	150	137	442	304
Commercial Lines | Bond
Segment Reporting Information [Line Items]
Earned premiums and fee income	68	67	206	192
Commercial Lines | Assumed reinsurance
Segment Reporting Information [Line Items]
Earned premiums and fee income	68	75	206	104
Commercial Lines | Automobile
Segment Reporting Information [Line Items]
Earned premiums and fee income	193	191	562	522
Personal Lines
Segment Reporting Information [Line Items]
Earned premiums and fee income	787	812	2,273	2,431
Personal Lines | AARP Members [Member]
Segment Reporting Information [Line Items]
Earned premiums and fee income	713	729	2,100	2,200
Personal Lines | Property
Segment Reporting Information [Line Items]
Earned premiums and fee income	240	248	721	741
Personal Lines | Automobile
Segment Reporting Information [Line Items]
Earned premiums and fee income	547	564	1,552	1,690
Group Benefits
Segment Reporting Information [Line Items]
Earned premiums and fee income	1,361	1,382	4,175	4,213
Group Benefits | Group disability
Segment Reporting Information [Line Items]
Earned premiums and fee income	697	697	2,142	2,124
Group Benefits | Group life
Segment Reporting Information [Line Items]
Earned premiums and fee income	594	621	1,833	1,902
Group Benefits | Other
Segment Reporting Information [Line Items]
Earned premiums and fee income	70	64	200	187
Hartford Funds
Segment Reporting Information [Line Items]
Earned premiums and fee income	250	254	724	743
Hartford Funds | Mutual fund and Exchange-Traded Products ("ETP")
Segment Reporting Information [Line Items]
Earned premiums and fee income	228	231	660	674
Hartford Funds | Talcott Resolution life and annuity separate accounts [2]
Segment Reporting Information [Line Items]
Earned premiums and fee income	$ 22	$ 23	$ 64	$ 69