Segments of Operations - Earnings before income taxes by segment and sub-segment (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Segment Reporting Information [Line Items]
Earnings before realized gains (losses) and income taxes		$ 229	$ 197	$ 496	$ 417
Realized gains (losses) on securities		31	8	(62)	11
Earnings before income taxes		260	205	434	428
Property and Casualty Insurance
Segment Reporting Information [Line Items]
Property and casualty insurance underwriting		72	72	163	150
Investment and other income, net	[1]	106	91	199	184
Earnings before realized gains (losses) and income taxes		178	163	362	334
Annuity
Segment Reporting Information [Line Items]
Earnings before realized gains (losses) and income taxes		99	85	224	181
Other
Segment Reporting Information [Line Items]
Earnings before realized gains (losses) and income taxes	[2]	(48)	(51)	(90)	(98)
Specialty Property and transportation | Property and Casualty Insurance
Segment Reporting Information [Line Items]
Property and casualty insurance underwriting		23	21	56	64
Specialty casualty | Property and Casualty Insurance
Segment Reporting Information [Line Items]
Property and casualty insurance underwriting		29	29	70	44
Specialty financial | Property and Casualty Insurance
Segment Reporting Information [Line Items]
Property and casualty insurance underwriting		22	23	37	45
Other specialty | Property and Casualty Insurance
Segment Reporting Information [Line Items]
Property and casualty insurance underwriting		(1)	0	2	(1)
Other lines | Property and Casualty Insurance
Segment Reporting Information [Line Items]
Property and casualty insurance underwriting		$ (1)	$ (1)	$ (2)	$ (2)

[1] Includes income of $13 million (before noncontrolling interest) from the sale of a hotel in the first quarter of 2017.

[2] Includes holding company interest and expenses, including a $7 million loss on retirement of debt in the second quarter of 2017.