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				345	(358)	323
Exercise of stock options					(37)
Share-based compensation expense and other					170
Funding of dividends declared to Retained earnings					(637)
Net income	$ 1,165						1,165
Funding of dividends declared from Additional paid-in capital							637
Dividends declared on Common Shares							(637)
Change in period, before reclassification from AOCI, net of income tax expense of $(259) and $(477)								1,375
Amounts reclassified from AOCI, net of income tax benefit of $3 and $5								155
Change in period, net of income tax expense of $(256) and $(472)								1,530
Change in period, net of income tax expense of $(7) and $(11)									382
Change in period, net of income tax benefit of $17 and $1										4
Balance - end of period at Jun. 30, 2016	47,226	11,121		(1,577)	15,858		20,643	2,404	(1,157)	(66)	$ 1,181
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				(475)
Net shares redeemed under employee share-based compensation plans				280	(275)	$ 0
Exercise of stock options					(38)
Share-based compensation expense and other					156
Funding of dividends declared to Retained earnings					(656)
Net income	2,398						2,398
Funding of dividends declared from Additional paid-in capital							656
Dividends declared on Common Shares							(656)
Change in period, before reclassification from AOCI, net of income tax expense of $(259) and $(477)								507
Amounts reclassified from AOCI, net of income tax benefit of $3 and $5								(14)
Change in period, net of income tax expense of $(256) and $(472)								493
Change in period, net of income tax expense of $(7) and $(11)									229
Change in period, net of income tax benefit of $17 and $1										(38)
Balance - end of period at Jun. 30, 2017	$ 50,349	$ 11,121		$ (1,675)	$ 14,522		$ 26,011	$ 1,551	$ (1,434)	$ 253	$ 370