Segment Information - Net Income (Details) - USD ($) $ in Millions	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]
Net income (loss)	$ 548	$ 535	$ 372	$ 630	$ 196	$ 432	$ 582	$ 597	$ 2,085	$ 1,807	$ (3,131)
Preferred stock dividends	5	11	0	5	6	0	0	0	21	6	0
Net income (loss) available to common stockholders	$ 543	$ 524	$ 372	$ 625	$ 190	$ 432	$ 582	$ 597	2,064	1,801	(3,131)
Commercial Lines
Segment Reporting Information [Line Items]
Net income (loss)									1,192	1,212	865
Personal Lines
Segment Reporting Information [Line Items]
Net income (loss)									318	(32)	(9)
Property & Casualty Other Operations
Segment Reporting Information [Line Items]
Net income (loss)									61	15	69
Group Benefits
Segment Reporting Information [Line Items]
Net income (loss)									536	340	294
Hartford Funds
Segment Reporting Information [Line Items]
Net income (loss)									149	148	106
Corporate
Segment Reporting Information [Line Items]
Net income (loss)									$ (171)	$ 124	$ (4,456)