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Segments of Operations - Earnings before income taxes by segment and sub-segment (Details) - USD ($) $ in Millions | 3 Months Ended
--- | ---
Mar. 31, 2018 | Mar. 31, 2017
Segment Reporting Information [Line Items] |  |  |
Earnings before realized gains (losses) and income taxes |  | $ 267 | $ 220
Realized gains (losses) on securities |  | (93) | 3
Earnings before income taxes |  | 174 | 223
Property and Casualty Insurance |  |  |
Segment Reporting Information [Line Items] |  |  |
Property and casualty insurance underwriting |  | 91 | 78
Investment and other income, net | [1] | 93 | 93
Earnings before realized gains (losses) and income taxes |  | 184 | 171
Annuity |  |  |
Segment Reporting Information [Line Items] |  |  |
Earnings before realized gains (losses) and income taxes |  | 125 | 96
Other |  |  |
Segment Reporting Information [Line Items] |  |  |
Earnings before realized gains (losses) and income taxes |  | (42) | (47)
Specialty Property and transportation | Property and Casualty Insurance |  |  |
Segment Reporting Information [Line Items] |  |  |
Property and casualty insurance underwriting |  | 33 | 43
Specialty casualty | Property and Casualty Insurance |  |  |
Segment Reporting Information [Line Items] |  |  |
Property and casualty insurance underwriting |  | 41 | 15
Specialty financial | Property and Casualty Insurance |  |  |
Segment Reporting Information [Line Items] |  |  |
Property and casualty insurance underwriting |  | 15 | 22
Other specialty | Property and Casualty Insurance |  |  |
Segment Reporting Information [Line Items] |  |  |
Property and casualty insurance underwriting |  | 3 | (1)
Other lines | Property and Casualty Insurance |  |  |
Segment Reporting Information [Line Items] |  |  |
Property and casualty insurance underwriting | [2] | $ (1) | $ (1)
[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.

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