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Unpaid losses and loss expenses Unpaid losses and loss expenses (PPD table) (Detail) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2019 | Jun. 30, 2018 | Jun. 30, 2019 | Jun. 30, 2018
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | $ (188) | $ (191) | $ (392) | $ (400)
North America Commercial P&C Insurance [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | (185) | (155) | (316) | (256)
North America Personal P&C Insurance [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | (16) | 7 | (26) | 1
North American Agriculture Insurance [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | 0 | 0 | (61) | (76)
Overseas General Insurance [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | (20) | (72) | (24) | (94)
Global Reinsurance [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | 0 | (16) | (8) | (30)
Corporate Segment [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | 33 | 45 | 43 | 55
Short Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | 18 | (100) | (130) | (327)
Short Tail [Member] | North America Commercial P&C Insurance [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | 21 | (51) | (45) | (160)
Short Tail [Member] | North America Personal P&C Insurance [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | (16) | 7 | (26) | 1
Short Tail [Member] | North American Agriculture Insurance [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | 0 | 0 | (61) | (76)
Short Tail [Member] | Overseas General Insurance [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | (20) | (70) | (24) | (92)
Short Tail [Member] | Global Reinsurance [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | 33 | 14 | 26 | 0
Short Tail [Member] | Corporate Segment [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | 0 | 0 | 0 | 0
Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | (206) | (91) | (262) | (73)
Long Tail [Member] | North America Commercial P&C Insurance [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | (206) | (104) | (271) | (96)
Long Tail [Member] | North America Personal P&C Insurance [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | 0 | 0 | 0 | 0
Long Tail [Member] | North American Agriculture Insurance [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | 0 | 0 | 0 | 0
Long Tail [Member] | Overseas General Insurance [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | 0 | (2) | 0 | (2)
Long Tail [Member] | Global Reinsurance [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | (33) | (30) | (34) | (30)
Long Tail [Member] | Corporate Segment [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | $ 33 | $ 45 | $ 43 | $ 55

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