Segment Information - Net Income (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Segment Reporting Information [Line Items]
Net income	$ 535	$ 432	$ 1,537	$ 1,611
Dividends declared on preferred stock	11	0	16	0
Net income available to common stockholders	524	432	1,521	1,611
Corporate
Segment Reporting Information [Line Items]
Net income	(99)	(35)	(142)	136
Property and Casualty, Commercial Insurance [Member]
Segment Reporting Information [Line Items]
Net income	336	289	890	959
Property and Casualty, Personal Insurance [Member]
Segment Reporting Information [Line Items]
Net income	94	51	252	146
Property & Casualty Other Operations
Segment Reporting Information [Line Items]
Net income	18	9	52	31
Group Insurance Policy [Member]
Segment Reporting Information [Line Items]
Net income	146	77	377	227
Mutual Fund [Member]
Segment Reporting Information [Line Items]
Net income	$ 40	$ 41	$ 108	$ 112