Segment Information - Net Income (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Net income (loss)	$ 196	$ 432	$ 582	$ 597	$ (3,703)	$ 234	$ (40)	$ 378	$ 1,807	$ (3,131)	$ 896
Preferred stock dividends	6	0	0	0	0	0	0	0	6	0	0
Net income (loss) available to common stockholders	$ 190	$ 432	$ 582	$ 597	$ (3,703)	$ 234	$ (40)	$ 378	1,801	(3,131)	896
Commercial Lines
Segment Reporting Information [Line Items]
Net income (loss)									1,212	865	994
Personal Lines
Segment Reporting Information [Line Items]
Net income (loss)									(32)	(9)	(9)
Property & Casualty Other Operations
Segment Reporting Information [Line Items]
Net income (loss)									15	69	(529)
Group Benefits
Segment Reporting Information [Line Items]
Net income (loss)									340	294	230
Hartford Funds
Segment Reporting Information [Line Items]
Net income (loss)									148	106	78
Corporate
Segment Reporting Information [Line Items]
Net income (loss)									$ 124	$ (4,456)	$ 132