Segment Information - Net Income (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Segment Reporting Information [Line Items]
Net income	$ 372	$ 582	$ 1,002	$ 1,179
Dividends declared on preferred stock	0	0	5	0
Net income available to common stockholders	372	582	997	1,179
Corporate
Segment Reporting Information [Line Items]
Net income	(43)	66	(43)	171
Property and Casualty, Commercial Insurance Product Line [Member]
Segment Reporting Information [Line Items]
Net income	191	372	554	670
Property and Casualty, Personal Insurance Product Line [Member]
Segment Reporting Information [Line Items]
Net income	62	6	158	95
Property & Casualty Other Operations
Segment Reporting Information [Line Items]
Net income	11	5	34	22
Group Insurance Policies [Member]
Segment Reporting Information [Line Items]
Net income	113	96	231	150
Mutual Fund [Member]
Segment Reporting Information [Line Items]
Net income	$ 38	$ 37	$ 68	$ 71

Amount of paid and unpaid preferred stock dividends declared with the form of settlement in cash.

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