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