Consolidated Statements Of Shareholders' Equity - USD ($) $ in Millions	Total	Common Stock [Member]	Common Stock [Member] The Chubb Corporation [Member]	Common shares in treasury [Member]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member] The Chubb Corporation [Member]	Retained Earnings [Member]	Accumulated Net Unrealized Investment Gain (Loss) [Member]	Cumulative Foreign Currency Translation Adjustment [Member]	Postretirement Benefit Liability Adjustment [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Balance - beginning of period at Dec. 31, 2015		$ 7,833		$ (1,922)	$ 4,481		$ 19,478	$ 874	$ (1,539)	$ (70)
Shares Issued for Chubb Corp Acquisition			$ 3,288			$ 11,916
Common Shares repurchased				0
Net shares redeemed under employee share-based compensation plans				372	(365)	323
Exercise of stock options					(44)
Share-based compensation expense and other					250
Funding of dividends declared to Retained earnings					(960)
Net income	$ 2,525						2,525
Funding of dividends declared from Additional paid-in capital							960
Dividends declared on Common Shares							(960)
Change in period, before reclassification from AOCI, net of income tax expense of $(310) and $(559)								1,540
Amounts reclassified from AOCI, net of income tax benefit of $3 and $16								133
Change in period, net of income tax expense of $(307) and $(543)								1,673
Change in period, net of income tax expense of $(14) and $(18)									251
Change in period, net of income tax benefit of $29 and nil										8
Balance - end of period at Sep. 30, 2016	48,372	11,121		(1,550)	15,601		22,003	2,547	(1,288)	(62)	$ 1,197
Balance - beginning of period at Dec. 31, 2016	48,275	11,121		(1,480)	15,335		23,613	1,058	(1,663)	291
Shares Issued for Chubb Corp Acquisition			$ 0			0
Common Shares repurchased				(707)
Net shares redeemed under employee share-based compensation plans				310	(311)	$ 0
Exercise of stock options					(43)
Share-based compensation expense and other					223
Funding of dividends declared to Retained earnings					(987)
Net income	2,328						2,328
Funding of dividends declared from Additional paid-in capital							987
Dividends declared on Common Shares							(987)
Change in period, before reclassification from AOCI, net of income tax expense of $(310) and $(559)								609
Amounts reclassified from AOCI, net of income tax benefit of $3 and $16								(24)
Change in period, net of income tax expense of $(307) and $(543)								585
Change in period, net of income tax expense of $(14) and $(18)									887
Change in period, net of income tax benefit of $29 and nil										(89)
Balance - end of period at Sep. 30, 2017	$ 50,471	$ 11,121		$ (1,877)	$ 14,217		$ 25,941	$ 1,643	$ (776)	$ 202	$ 1,069