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Claim and Claim Adjustment Expense Reserves (International - Hardy - Net Strengthening or Releasing of Prior Accident Year Reserves) (Details) - International - Hardy - USD ($) $ in Millions | 12 Months Ended | 24 Months Ended | 36 Months Ended | 48 Months Ended | 60 Months Ended
--- | --- | --- | --- | --- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012 | Dec. 31, 2016 | Dec. 31, 2016 | Dec. 31, 2016 | Dec. 31, 2016
2008 |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | $ 1 | $ (1) | $ 0 | $ 2 | $ (4) | $ (3) |  |  |  | $ (5)
2009 |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | (1) | (3) | 5 | (11) | (5) | 0 |  |  |  | (15)
2010 |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | (1) | 6 | (6) | 5 | 9 | (10) |  |  |  | 3
2011 |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | 0 | 0 | 4 | 0 | 10 | $ 0 |  |  |  | 14
2012 |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | 1 | (7) | 8 | 7 | $ 1 |  |  |  |  | $ 10
2013 |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | 1 | 1 | (8) | $ 15 |  |  |  |  | $ 9 |
2014 |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | (7) | (6) | $ (2) |  |  |  |  | $ (15) |  |
2015 |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | (2) | $ (10) |  |  |  |  | $ (12) |  |  |
2016 |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | $ 19 |  |  |  |  |  |  |  |  |

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