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Segments of Operations - Revenues by segment and sub-segment (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2017 | Sep. 30, 2017 | Jun. 30, 2017 | Mar. 31, 2017 | Dec. 31, 2016 | Sep. 30, 2016 | Jun. 30, 2016 | Mar. 31, 2016 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Total premiums earned |  |  |  |  |  |  |  |  |  | $ 4,579 | $ 4,328 | $ 4,224
Net investment income |  |  |  |  |  |  |  |  |  | 1,831 | 1,696 | 1,633
Other income |  |  |  |  |  |  |  |  |  | 206 | 224 | 243
Revenues before realized gains (losses) |  |  |  |  |  |  |  |  |  | 6,860 | 6,477 | 6,325
Realized gains (losses) on securities |  |  |  |  |  |  |  |  |  | 5 | 19 | (19)
Realized gains (losses) on subsidiaries |  |  |  |  |  |  |  |  |  | 0 | 2 | (161)
Total revenues |  | $ 1,808 | $ 1,835 | $ 1,646 | $ 1,576 | $ 1,737 | $ 1,705 | $ 1,581 | $ 1,475 | 6,865 | 6,498 | 6,145
Property and casualty insurance |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Total premiums earned |  |  |  |  |  |  |  |  |  | 4,579 | 4,328 | 4,224
Net investment income |  |  |  |  |  |  |  |  |  | 362 | 350 | 319
Other income | [1] |  |  |  |  |  |  |  |  | 28 | 51 | 78
Revenues before realized gains (losses) |  |  |  |  |  |  |  |  |  | 4,969 | 4,729 | 4,621
Annuity |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Net investment income |  |  |  |  |  |  |  |  |  | 1,458 | 1,356 | 1,224
Other income |  |  |  |  |  |  |  |  |  | 103 | 103 | 98
Revenues before realized gains (losses) |  |  |  |  |  |  |  |  |  | 1,561 | 1,459 | 1,322
Run-off long-term care and life |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues before realized gains (losses) | [2] |  |  |  |  |  |  |  |  | 47 | 49 | 188
Other |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues before realized gains (losses) |  |  |  |  |  |  |  |  |  | 283 | 240 | 194
Property and transportation | Property and casualty insurance |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Total premiums earned |  |  |  |  |  |  |  |  |  | 1,711 | 1,662 | 1,599
Specialty casualty | Property and casualty insurance |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Total premiums earned |  |  |  |  |  |  |  |  |  | 2,186 | 2,006 | 2,011
Specialty financial | Property and casualty insurance |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Total premiums earned |  |  |  |  |  |  |  |  |  | 576 | 557 | 517
Other specialty | Property and casualty insurance |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Total premiums earned |  |  |  |  |  |  |  |  |  | $ 106 | $ 103 | $ 97
[1] | Includes income of $32 million (before noncontrolling interest) from the sale of an apartment property in 2016 and $66 million (before noncontrolling interest) from the sales of a hotel and an apartment property in 2015.
[2] | AFG sold substantially all of its run-off long-term care insurance business in December 2015.

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