Information provided in connection with outstanding debt of subsidiaries (Condensed Consolidating Statement Of Operations and Comprehensive Income) (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Information Provided In Connection With Outstanding Debt Of Subsidiaries [Line Items]
Net premiums written									$ 29,244	$ 28,145	$ 17,713
Net premiums earned	$ 7,218	$ 7,807	$ 7,237	$ 6,772	$ 7,059	$ 7,688	$ 7,405	$ 6,597	29,034	28,749	17,213
Net Investment Income	797	813	770	745	744	739	708	674	3,125	2,865	2,194
Net realized gains (losses) including OTTI	0	(10)	101	(7)	365	100	(216)	(394)	84	(145)	(420)
Losses and loss expenses	4,272	6,247	4,146	3,789	3,855	4,269	4,254	3,674	18,454	16,052	9,484
Policy benefits	176	169	163	168	161	155	146	126	676	588	543
Policy acquisition costs and administrative expenses									8,614	8,985	5,211
Interest (income) expense									607	605	300
Other (Income) Expense									(400)	(222)	(51)
Amortization of Purchased Intangibles									260	19	171
Chubb integration expenses									310	492	33
Income tax expense									(139)	815	462
Net income	$ 1,533	$ (70)	$ 1,305	$ 1,093	$ 1,610	$ 1,360	$ 726	$ 439	3,861	4,135	2,834
Comprehensive income									4,718	4,556	908
Chubb limited (Parent Guarantor)
Information Provided In Connection With Outstanding Debt Of Subsidiaries [Line Items]
Net premiums written											0
Net premiums earned											0
Net Investment Income									4	3	3
Equity in earnings of subsidiaries									3,640	3,901	2,673
Net realized gains (losses) including OTTI									0	0	0
Losses and loss expenses											0
Policy benefits											0
Policy acquisition costs and administrative expenses									75	64	63
Interest (income) expense									(332)	(353)	(32)
Other (Income) Expense									(12)	(25)	(208)
Amortization of Purchased Intangibles									0	0	0
Chubb integration expenses									32	62	3
Income tax expense									20	21	16
Net income									3,861	4,135	2,834
Comprehensive income									4,718	4,556	908
Chubb INA Holdings Inc. (Subsidiary Issuer)
Information Provided In Connection With Outstanding Debt Of Subsidiaries [Line Items]
Net premiums written									0	0	0
Net premiums earned									0	0	0
Net Investment Income									14	11	4
Equity in earnings of subsidiaries									2,424	2,555	1,038
Net realized gains (losses) including OTTI									(25)	3	(9)
Losses and loss expenses									0	0	0
Policy benefits									0	0	0
Policy acquisition costs and administrative expenses									40	82	28
Interest (income) expense									847	908	302
Other (Income) Expense									93	35	(4)
Amortization of Purchased Intangibles									0	0	0
Chubb integration expenses									69	126	29
Income tax expense									(742)	(416)	(349)
Net income									2,106	1,834	1,027
Comprehensive income									3,075	2,001	(192)
Other Chubb Limited Subsidiaries and Eliminations
Information Provided In Connection With Outstanding Debt Of Subsidiaries [Line Items]
Net premiums written									29,244	28,145	17,713
Net premiums earned									29,034	28,749	17,213
Net Investment Income									3,107	2,851	2,187
Equity in earnings of subsidiaries											0
Net realized gains (losses) including OTTI									109	(148)	(411)
Losses and loss expenses									18,454	16,052	9,484
Policy benefits									676	588	543
Policy acquisition costs and administrative expenses									8,499	8,839	5,120
Interest (income) expense									92	50	30
Other (Income) Expense									(481)	(232)	161
Amortization of Purchased Intangibles									260	19	171
Chubb integration expenses									209	304	1
Income tax expense									583	1,210	795
Net income									3,958	4,622	2,684
Comprehensive income									4,430	5,045	757
Consolidating Adjustments
Information Provided In Connection With Outstanding Debt Of Subsidiaries [Line Items]
Net premiums written											0
Net premiums earned											0
Equity in earnings of subsidiaries									(6,064)	(6,456)	(3,711)
Net realized gains (losses) including OTTI									0	0	0
Losses and loss expenses											0
Policy benefits											0
Policy acquisition costs and administrative expenses											0
Interest (income) expense											0
Amortization of Purchased Intangibles									0	0	0
Chubb integration expenses									0	0
Income tax expense										0	0
Net income									(6,064)	(6,456)	(3,711)
Comprehensive income									$ (7,505)	$ (7,046)	$ (565)