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Reinsurance (Consolidated Reinsurance) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Premiums written [Abstract] |  |  |
Direct | $ 37,749 | $ 36,848 | $ 34,782
Assumed | 3,512 | 3,276 | 3,186
Ceded | (7,441) | (7,849) | (7,389)
Net | 33,820 | 32,275 | 30,579
Premiums earned [Abstract] |  |  |
Direct | 37,037 | 35,876 | 34,108
Assumed | 3,323 | 3,107 | 3,175
Ceded | (7,243) | (7,693) | (7,219)
Net premiums earned | 33,117 | 31,290 | 30,064
Reinsurance recoveries on losses and loss expenses incurred | $ 5,000 | $ 4,900 | $ 5,600

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