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Claim and Claim Adjustment Expense Reserves (International - Excluding Hardy - Net Incurred Claims and Allocated Claim Adjustment Expenses) (Details) - Excluding Hardy - International $ in Millions | Dec. 31, 2017 USD ($) claims | Dec. 31, 2016 USD ($) | Dec. 31, 2015 USD ($) | Dec. 31, 2014 USD ($) | Dec. 31, 2013 USD ($) | Dec. 31, 2012 USD ($) | Dec. 31, 2011 USD ($) | Dec. 31, 2010 USD ($) | Dec. 31, 2009 USD ($) | Dec. 31, 2008 USD ($)
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Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net | $ 2,676 |  |  |  |  |  |  |  |  |
IBNR | 563 |  |  |  |  |  |  |  |  |
2008 |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net | 224 | $ 225 | $ 229 | $ 227 | $ 218 | $ 226 | $ 226 | $ 234 | $ 246 | $ 243
IBNR | $ 7 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | claims | 25,185 |  |  |  |  |  |  |  |  |
2009 |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net | $ 232 | 233 | 242 | 252 | 256 | 271 | 270 | 268 | $ 272 |
IBNR | $ 7 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | claims | 21,402 |  |  |  |  |  |  |  |  |
2010 |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net | $ 202 | 208 | 215 | 222 | 232 | 239 | 244 | $ 247 |  |
IBNR | $ 13 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | claims | 22,943 |  |  |  |  |  |  |  |  |
2011 |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net | $ 232 | 235 | 242 | 253 | 275 | 283 | $ 281 |  |  |
IBNR | $ 11 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | claims | 25,448 |  |  |  |  |  |  |  |  |
2012 |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net | $ 259 | 267 | 266 | 273 | 289 | $ 282 |  |  |  |
IBNR | $ 28 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | claims | 25,450 |  |  |  |  |  |  |  |  |
2013 |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net | $ 273 | 278 | 298 | 307 | $ 304 |  |  |  |  |
IBNR | $ 43 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | claims | 24,276 |  |  |  |  |  |  |  |  |
2014 |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net | $ 296 | 308 | 308 | $ 292 |  |  |  |  |  |
IBNR | $ 68 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | claims | 25,343 |  |  |  |  |  |  |  |  |
2015 |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net | $ 321 | 323 | $ 307 |  |  |  |  |  |  |
IBNR | $ 88 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | claims | 23,563 |  |  |  |  |  |  |  |  |
2016 |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net | $ 320 | $ 301 |  |  |  |  |  |  |  |
IBNR | $ 120 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | claims | 17,166 |  |  |  |  |  |  |  |  |
2017 |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net | $ 317 |  |  |  |  |  |  |  |  |
IBNR | $ 178 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | claims | 14,772 |  |  |  |  |  |  |  |  |

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