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Segments of Operations - Revenues by segment and sub-segment (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2017 | Jun. 30, 2016 | Jun. 30, 2017 | Jun. 30, 2016
Segment Reporting Information [Line Items] |  |  |  |  |
Total premiums earned |  | $ 1,065 | $ 1,027 | $ 2,087 | $ 2,025
Net investment income |  | 460 | 423 | 895 | 834
Other income |  | 47 | 80 | 106 | 126
Revenues before realized gains (losses) |  | 1,638 | 1,595 | 3,211 | 3,088
Realized gains (losses) on securities |  | 8 | (16) | 11 | (34)
Realized gains on subsidiaries |  | 0 | 2 | 0 | 2
Total revenues |  | 1,646 | 1,581 | 3,222 | 3,056
Property and Casualty Insurance |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Total premiums earned |  | 1,065 | 1,027 | 2,087 | 2,025
Net investment income |  | 96 | 89 | 182 | 172
Other income | [1] | 4 | 40 | 20 | 43
Revenues before realized gains (losses) |  | 1,165 | 1,156 | 2,289 | 2,240
Annuity |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Net investment income |  | 360 | 344 | 707 | 659
Other income |  | 26 | 24 | 53 | 50
Revenues before realized gains (losses) |  | 386 | 368 | 760 | 709
Run-off Long-term Care and Life |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Revenues before realized gains (losses) |  | 11 | 12 | 23 | 24
Other |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Revenues before realized gains (losses) |  | 76 | 59 | 139 | 115
Specialty Property and transportation | Property and Casualty Insurance |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Total premiums earned |  | 357 | 365 | 699 | 704
Specialty casualty | Property and Casualty Insurance |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Total premiums earned |  | 537 | 497 | 1,045 | 999
Specialty financial | Property and Casualty Insurance |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Total premiums earned |  | 146 | 139 | 293 | 271
Other specialty | Property and Casualty Insurance |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Total premiums earned |  | $ 25 | $ 26 | $ 50 | $ 51
[1] | Includes pretax income of $13 million (before noncontrolling interest) from the sale of a hotel in the first quarter of 2017 and pretax income of $32 million (before noncontrolling interest) from the sale of an apartment property in the second quarter of 2016.

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