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				274	(310)	323
Exercise of stock options					(21)
Share-based compensation expense and other					65
Funding of dividends declared to Retained earnings					(314)
Net income	$ 439						439
Funding of dividends declared from Additional paid-in capital							314
Dividends declared on Common Shares							(314)
Change in period, before reclassification from AOCI, net of income tax expense of $(102) and $(232)								673
Amounts reclassified from AOCI, net of income tax expense of $(6) and $(1)								151
Change in period, net of income tax expense of $(108) and $(233)								824
Change in period, net of income tax expense of $(3) and $(35)									277
Change in period, net of income tax expense of $(4) and $(1)										1
Balance - end of period at Mar. 31, 2016	45,897	11,121		(1,648)	16,140		19,917	1,698	(1,262)	(69)	$ 367
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				(140)
Net shares redeemed under employee share-based compensation plans				222	(260)	$ 0
Exercise of stock options					(21)
Share-based compensation expense and other					65
Funding of dividends declared to Retained earnings					(324)
Net income	1,093						1,093
Funding of dividends declared from Additional paid-in capital							324
Dividends declared on Common Shares							(324)
Change in period, before reclassification from AOCI, net of income tax expense of $(102) and $(232)								205
Amounts reclassified from AOCI, net of income tax expense of $(6) and $(1)								2
Change in period, net of income tax expense of $(108) and $(233)								207
Change in period, net of income tax expense of $(3) and $(35)									131
Change in period, net of income tax expense of $(4) and $(1)										(24)
Balance - end of period at Mar. 31, 2017	$ 49,224	$ 11,121		$ (1,398)	$ 14,795		$ 24,706	$ 1,265	$ (1,532)	$ 267	$ 0