Segment Information - Net Income (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Segment Reporting Information [Line Items]
Net income	$ 630	$ 597
Dividends declared on preferred stock	5	0
Net Income (Loss) Available to Common Stockholders, Basic	625	597
Corporate
Segment Reporting Information [Line Items]
Net income	0	105
Property and Casualty, Commercial Insurance Product Line [Member]
Segment Reporting Information [Line Items]
Net income	363	298
Property and Casualty, Personal Insurance Product Line [Member]
Segment Reporting Information [Line Items]
Net income	96	89
Property & Casualty Other Operations
Segment Reporting Information [Line Items]
Net income	23	17
Group Insurance Policies [Member]
Segment Reporting Information [Line Items]
Net income	118	54
Mutual Fund [Member]
Segment Reporting Information [Line Items]
Net income	$ 30	$ 34