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Consolidated Statements Of Shareholders' Equity - USD ($) $ in Millions | Total | Common Shares | Common Shares in Treasury | Additional Paid-in Capital | Retained Earnings | Net unrealized appreciation on investments | Cumulative Translation Adjustment | Accumulated Defined Benefit Plans Adjustment [Member] | Accumulated Other Comprehensive Income | The Chubb Corporation [Member] Common Shares | The Chubb Corporation [Member] Additional Paid-in Capital
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Balance – beginning of year at Dec. 31, 2015 |  | $ 7,833 | $ (1,922) | $ 4,481 | $ 19,478 | $ 874 | $ (1,539) | $ (70) |  |  |
Common Shares repurchased | $ 0 |  | 0 |  |  |  |  |  |  |  |
Shares issued for Chubb Corp acquisition |  |  |  |  |  |  |  |  |  | $ 3,288 | $ 11,916
Net shares redeemed under employee share-based compensation plans |  |  | 442 | (382) |  |  |  |  |  |  | 323
Stock Issued During Period, Value, Stock Options Exercised |  |  |  | (64) |  |  |  |  |  |  |
Share-based compensation expense |  |  |  | 313 |  |  |  |  |  |  |
FundingDividendsDeclaredToRetainedEarnings |  |  |  | (1,284) |  |  |  |  |  |  |
Tax benefit on share-based compensation expense |  |  |  | 32 |  |  |  |  |  |  |
Net income | 4,135 |  |  |  | 4,135 |  |  |  |  |  |
Funding Dividends Declared From Additional Paid In Capital |  |  |  |  | 1,284 |  |  |  |  |  |
Dividends declared on Common Shares |  |  |  |  | (1,284) |  |  |  |  |  |
Change in year, before reclassification from AOCI, net of income tax benefit (expense) of $338, $(228), and $72 |  |  |  |  |  | 37 |  |  |  |  |
Amounts reclassified from AOCI, net of income tax benefit (expense) of $(41), $(13), and $28 |  |  |  |  |  | 147 |  |  |  |  |
Change in year, net of income tax benefit (expense) of $297, $(241), and $100 |  |  |  |  |  | 184 |  |  |  |  |
Change in year, net of income tax benefit of $35, $5, and $30 |  |  |  |  |  |  | (124) |  |  |  |
Change in year, net of income tax benefit (expense) of $67, $5, and $(184) |  |  |  |  |  |  |  | 361 |  |  |
Balance – Ending of year at Dec. 31, 2016 | 48,275 | 11,121 | (1,480) | 15,335 | 23,613 | 1,058 | (1,663) | 291 | $ (314) |  |
Common Shares repurchased |  |  | (830) |  |  |  |  |  |  |  |
Shares issued for Chubb Corp acquisition |  |  |  |  |  |  |  |  |  | 0 | 0
Net shares redeemed under employee share-based compensation plans |  |  | 366 | (313) |  |  |  |  |  |  |
Stock Issued During Period, Value, Stock Options Exercised |  |  |  | (58) |  |  |  |  |  |  |
Share-based compensation expense |  |  |  | 331 |  |  |  |  |  |  |
FundingDividendsDeclaredToRetainedEarnings |  |  |  | (1,317) |  |  |  |  |  |  |
Tax benefit on share-based compensation expense |  |  |  | 0 |  |  |  |  |  |  |
Net income | 3,861 |  |  |  | 3,861 |  |  |  |  |  |
Funding Dividends Declared From Additional Paid In Capital |  |  |  |  | 1,317 |  |  |  |  |  |
Dividends declared on Common Shares |  |  |  |  | (1,317) |  |  |  |  |  |
Change in year, before reclassification from AOCI, net of income tax benefit (expense) of $338, $(228), and $72 |  |  |  |  |  | 390 |  |  |  |  |
Amounts reclassified from AOCI, net of income tax benefit (expense) of $(41), $(13), and $28 |  |  |  |  |  | 2 |  |  |  |  |
Change in year, net of income tax benefit (expense) of $297, $(241), and $100 |  |  |  |  |  | 392 |  |  |  |  |
Change in year, net of income tax benefit of $35, $5, and $30 |  |  |  |  |  |  | 476 |  |  |  |
Change in year, net of income tax benefit (expense) of $67, $5, and $(184) |  |  |  |  |  |  |  | (11) |  |  |
Balance – Ending of year at Dec. 31, 2017 | 51,172 | 11,121 | (1,944) | 13,978 | 27,738 | 1,154 | (1,209) | 327 | 543 |  |
Balance – Ending of year (Previous Accounting Guidance [Member]) at Dec. 31, 2017 |  |  |  |  | 27,474 | 1,450 | (1,187) | 280 |  |  |
Cumulative Effect of New Accounting Principle in Period of Adoption |  |  |  |  | 264 | (296) |  |  |  |  |
Common Shares repurchased |  |  | (1,021) |  |  |  |  |  |  |  |
Shares issued for Chubb Corp acquisition |  |  |  |  |  |  |  |  |  | $ 0 | $ 0
Net shares redeemed under employee share-based compensation plans |  |  | 347 | (313) |  |  |  |  |  |  |
Stock Issued During Period, Value, Stock Options Exercised |  |  |  | (49) |  |  |  |  |  |  |
Share-based compensation expense |  |  |  | 285 |  |  |  |  |  |  |
FundingDividendsDeclaredToRetainedEarnings |  |  |  | (1,344) |  |  |  |  |  |  |
Tax benefit on share-based compensation expense |  |  |  | 0 |  |  |  |  |  |  |
Net income | 3,962 |  |  |  | 3,962 |  |  |  |  |  |
Funding Dividends Declared From Additional Paid In Capital |  |  |  |  | 1,344 |  |  |  |  |  |
Dividends declared on Common Shares |  |  |  |  | (1,344) |  |  |  |  |  |
Change in year, before reclassification from AOCI, net of income tax benefit (expense) of $338, $(228), and $72 |  |  |  |  |  | (1,960) |  |  |  |  |
Amounts reclassified from AOCI, net of income tax benefit (expense) of $(41), $(13), and $28 |  |  |  |  |  | 261 |  |  |  |  |
Change in year, net of income tax benefit (expense) of $297, $(241), and $100 |  |  |  |  |  | (1,699) |  |  |  |  |
Change in year, net of income tax benefit of $35, $5, and $30 |  |  |  |  |  |  | (767) |  |  |  |
Change in year, net of income tax benefit (expense) of $67, $5, and $(184) |  |  |  |  |  |  |  | (254) |  |  |
Balance – Ending of year at Dec. 31, 2018 | $ 50,312 | $ 11,121 | $ (2,618) | $ 12,557 | 31,700 | (545) | (1,976) | 73 | $ (2,448) |  |
Cumulative Effect of New Accounting Principle in Period of Adoption | Accounting standards update 2018-02 [Member] |  |  |  |  | $ (146) | $ 121 | $ (22) | $ 47 |  |  |

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