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, 2014		$ 8,055	$ (1,448)	$ 5,145	$ 16,644	$ 1,851	$ (581)	$ (79)
Dividends declared on Common Shares – par value reduction		(222)
Common Shares repurchased			(734)
Shares issued for Chubb Corp acquisition										$ 0	$ 0
Net shares redeemed under employee share-based compensation plans			260	(160)
Stock Issued During Period, Value, Stock Options Exercised				(61)
Share-based compensation expense and other				184
Funding of dividends declared from Additional paid-in capital				(653)	653
Tax benefit on share-based compensation expense				26
Net income	$ 2,834				2,834
Dividends declared on Common Shares					(653)
Change in year, before reclassification from AOCI, net of income tax benefit (expense) of $(228), $72, and $154						(1,126)
Amounts reclassified from AOCI, net of income tax benefit (expense) of $(13), $28, and $(2)						149
Change in year, net of income tax benefit (expense) of $(241), $100, and $152						(977)
Change in year, net of income tax benefit of $5, $30, and nil							(958)
Change in year, net of income tax benefit (expense) of $5, $(184), and $(6)								9
Balance – Ending of year at Dec. 31, 2015	29,135	7,833	(1,922)	4,481	19,478	874	(1,539)	(70)	$ (735)
Common Shares repurchased			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 and other				313
Funding of dividends declared from Additional paid-in capital				(1,284)	1,284
Tax benefit on share-based compensation expense				32
Net income	4,135				4,135
Dividends declared on Common Shares					(1,284)
Change in year, before reclassification from AOCI, net of income tax benefit (expense) of $(228), $72, and $154						37
Amounts reclassified from AOCI, net of income tax benefit (expense) of $(13), $28, and $(2)						147
Change in year, net of income tax benefit (expense) of $(241), $100, and $152						184
Change in year, net of income tax benefit of $5, $30, and nil							(124)
Change in year, net of income tax benefit (expense) of $5, $(184), and $(6)								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 and other				331
Funding of dividends declared from Additional paid-in capital				(1,317)	1,317
Net income	3,861				3,861
Dividends declared on Common Shares					(1,317)
Change in year, before reclassification from AOCI, net of income tax benefit (expense) of $(228), $72, and $154						390
Amounts reclassified from AOCI, net of income tax benefit (expense) of $(13), $28, and $(2)						2
Change in year, net of income tax benefit (expense) of $(241), $100, and $152						392
Change in year, net of income tax benefit of $5, $30, and nil							476
Change in year, net of income tax benefit (expense) of $5, $(184), and $(6)								(11)
Balance – Ending of year at Dec. 31, 2017	$ 51,172	$ 11,121	$ (1,944)	$ 13,978	$ 27,474	$ 1,450	$ (1,187)	$ 280	$ 543