Segment Information - Revenues (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Earned premiums and fee income									$ 18,224,000,000	$ 17,182,000,000	$ 15,309,000,000
Total net investment income									1,951,000,000	1,780,000,000	1,603,000,000
Net realized capital gains (losses)									395,000,000	(112,000,000)	165,000,000
Other revenues									170,000,000	105,000,000	85,000,000
Total revenues	$ 5,361,000,000	$ 5,347,000,000	$ 5,092,000,000	$ 4,940,000,000	$ 4,633,000,000	$ 4,842,000,000	$ 4,789,000,000	$ 4,691,000,000	20,740,000,000	18,955,000,000	17,162,000,000
Property and Casualty, Commercial Insurance [Member]
Segment Reporting Information [Line Items]
Earned premiums and fee income									8,325,000,000	7,081,000,000	6,902,000,000
Total net investment income									1,129,000,000	997,000,000	949,000,000
Property and Casualty, Commercial Insurance [Member] | Workers’ compensation
Segment Reporting Information [Line Items]
Earned premiums and fee income									3,314,000,000	3,341,000,000	3,287,000,000
Property and Casualty, Commercial Insurance [Member] | Liability
Segment Reporting Information [Line Items]
Earned premiums and fee income									1,064,000,000	653,000,000	604,000,000
Property and Casualty, Commercial Insurance [Member] | Marine [Member]
Segment Reporting Information [Line Items]
Earned premiums and fee income									147,000,000	0	0
Property and Casualty, Commercial Insurance [Member] | Package business
Segment Reporting Information [Line Items]
Earned premiums and fee income									1,471,000,000	1,364,000,000	1,301,000,000
Property and Casualty, Commercial Insurance [Member] | Property
Segment Reporting Information [Line Items]
Earned premiums and fee income									728,000,000	618,000,000	604,000,000
Property and Casualty, Commercial Insurance [Member] | Professional liability
Segment Reporting Information [Line Items]
Earned premiums and fee income									447,000,000	254,000,000	246,000,000
Property and Casualty, Commercial Insurance [Member] | Bond
Segment Reporting Information [Line Items]
Earned premiums and fee income									261,000,000	241,000,000	230,000,000
Property and Casualty, Commercial Insurance [Member] | Assumed Reinsurance [Member]
Segment Reporting Information [Line Items]
Earned premiums and fee income									180,000,000	0	0
Property and Casualty, Commercial Insurance [Member] | Automobile
Segment Reporting Information [Line Items]
Earned premiums and fee income									713,000,000	610,000,000	630,000,000
Property and Casualty, Personal Insurance [Member]
Segment Reporting Information [Line Items]
Earned premiums and fee income									3,235,000,000	3,439,000,000	3,734,000,000
Total net investment income									179,000,000	155,000,000	141,000,000
Property and Casualty, Personal Insurance [Member] | AARP Members
Segment Reporting Information [Line Items]
Earned premiums and fee income									2,900,000,000	3,000,000,000.0	3,200,000,000
Property and Casualty, Personal Insurance [Member] | Property
Segment Reporting Information [Line Items]
Earned premiums and fee income									987,000,000	1,041,000,000	1,117,000,000
Property and Casualty, Personal Insurance [Member] | Automobile
Segment Reporting Information [Line Items]
Earned premiums and fee income									2,248,000,000	2,398,000,000	2,617,000,000
Property & Casualty Other Operations
Segment Reporting Information [Line Items]
Earned premiums and fee income									2,000,000	0	0
Total net investment income									84,000,000	90,000,000	106,000,000
Group Benefits
Segment Reporting Information [Line Items]
Earned premiums and fee income									5,603,000,000	5,598,000,000	3,677,000,000
Total net investment income									486,000,000	474,000,000	381,000,000
Group Benefits | Group disability
Segment Reporting Information [Line Items]
Earned premiums and fee income									2,828,000,000	2,746,000,000	1,718,000,000
Group Benefits | Group life
Segment Reporting Information [Line Items]
Earned premiums and fee income									2,521,000,000	2,611,000,000	1,745,000,000
Group Benefits | Other
Segment Reporting Information [Line Items]
Earned premiums and fee income									254,000,000	241,000,000	214,000,000
Hartford Funds
Segment Reporting Information [Line Items]
Earned premiums and fee income									999,000,000	1,032,000,000	992,000,000
Total net investment income									7,000,000	5,000,000	3,000,000
Hartford Funds | Third party retail customers [Member]
Segment Reporting Information [Line Items]
Earned premiums and fee income									907,000,000	932,000,000	888,000,000
Hartford Funds | Talcott Resolution [Member]
Segment Reporting Information [Line Items]
Earned premiums and fee income									92,000,000	100,000,000	104,000,000
Corporate
Segment Reporting Information [Line Items]
Earned premiums and fee income									60,000,000	32,000,000	4,000,000
Total net investment income									$ 66,000,000	$ 59,000,000	23,000,000
Accounting Standards Update 2014-09 [Member] | Operating Expense [Member]
Segment Reporting Information [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Change on Net Income											$ 188