Segment Information - Net Investment Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Net investment income	$ 1,951	$ 1,780	$ 1,603
Property and Casualty, Commercial Insurance [Member]
Segment Reporting Information [Line Items]
Net investment income	1,129	997	949
Property and Casualty, Personal Insurance [Member]
Segment Reporting Information [Line Items]
Net investment income	179	155	141
Property & Casualty Other Operations
Segment Reporting Information [Line Items]
Net investment income	84	90	106
Group Benefits
Segment Reporting Information [Line Items]
Net investment income	486	474	381
Hartford Funds
Segment Reporting Information [Line Items]
Net investment income	7	5	3
Corporate
Segment Reporting Information [Line Items]
Net investment income	$ 66	$ 59	$ 23