v3.2.0.727
Segment Information (Net Premiums Earned For Segment By Product) (Detail) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2015
Jun. 30, 2014
Jun. 30, 2015
Jun. 30, 2014
Segment Reporting Information [Line Items]        
Property & All Other $ 1,659 $ 1,612 $ 2,978 $ 2,967
Casualty 1,588 1,542 3,094 3,022
Life, Accident & Health 1,113 1,178 2,215 2,313
Net premiums earned 4,360 4,332 8,287 8,302
Insurance - North American P&C [Member]        
Segment Reporting Information [Line Items]        
Net premiums earned 1,688 1,542 3,214 3,029
Insurance - North American P&C [Member] | Property Insurance Product Line [Member]        
Segment Reporting Information [Line Items]        
Net premiums earned 507 423 917 828
Insurance - North American P&C [Member] | Casualty Insurance Product Line [Member]        
Segment Reporting Information [Line Items]        
Net premiums earned 1,079 1,018 2,094 1,999
Insurance - North American P&C [Member] | Life Accident And Health Product Line [Member]        
Segment Reporting Information [Line Items]        
Net premiums earned 102 101 203 202
Insurance - North American Agriculture [Member]        
Segment Reporting Information [Line Items]        
Net premiums earned 321 330 385 433
Insurance - North American Agriculture [Member] | Property Insurance Product Line [Member]        
Segment Reporting Information [Line Items]        
Net premiums earned 321 330 385 433
Insurance - North American Agriculture [Member] | Casualty Insurance Product Line [Member]        
Segment Reporting Information [Line Items]        
Net premiums earned 0 0 0 0
Insurance - North American Agriculture [Member] | Life Accident And Health Product Line [Member]        
Segment Reporting Information [Line Items]        
Net premiums earned 0 0 0 0
Insurance - Overseas General [Member]        
Segment Reporting Information [Line Items]        
Net premiums earned 1,644 1,709 3,281 3,321
Insurance - Overseas General [Member] | Property Insurance Product Line [Member]        
Segment Reporting Information [Line Items]        
Net premiums earned 729 727 1,457 1,420
Insurance - Overseas General [Member] | Casualty Insurance Product Line [Member]        
Segment Reporting Information [Line Items]        
Net premiums earned 391 395 773 764
Insurance - Overseas General [Member] | Life Accident And Health Product Line [Member]        
Segment Reporting Information [Line Items]        
Net premiums earned 524 587 1,051 1,137
Global Reinsurance [Member]        
Segment Reporting Information [Line Items]        
Net premiums earned 220 261 446 545
Global Reinsurance [Member] | Property Insurance Product Line [Member]        
Segment Reporting Information [Line Items]        
Net premiums earned 102 132 219 286
Global Reinsurance [Member] | Casualty Insurance Product Line [Member]        
Segment Reporting Information [Line Items]        
Net premiums earned 118 129 227 259
Global Reinsurance [Member] | Life Accident And Health Product Line [Member]        
Segment Reporting Information [Line Items]        
Net premiums earned 0 0 0 0
Life [Member]        
Segment Reporting Information [Line Items]        
Net premiums earned 487 490 961 974
Life [Member] | Property Insurance Product Line [Member]        
Segment Reporting Information [Line Items]        
Net premiums earned 0 0 0 0
Life [Member] | Casualty Insurance Product Line [Member]        
Segment Reporting Information [Line Items]        
Net premiums earned 0 0 0 0
Life [Member] | Life Accident And Health Product Line [Member]        
Segment Reporting Information [Line Items]        
Net premiums earned $ 487 $ 490 $ 961 $ 974