Schedule II Schedule II (STATEMENTS OF OPERATIONS - Parent Company Only) (Details) - 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
Condensed Financial Statements, Captions [Line Items]
Equity in net income of subsidiaries and affiliates									$ 418	$ 264	$ 113
Net realized gains (losses)	$ 0	$ (10)	$ 101	$ (7)	$ 365	$ 100	$ (216)	$ (394)	84	(145)	(420)
Total revenues	8,015	8,610	8,108	7,510	8,168	8,527	7,897	6,877	32,243	31,469	18,987
Administrative and other (income) expense									2,833	3,081	2,270
Business Combination, Integration Related Costs									310	492	33
Income tax expense (benefit)									(139)	815	462
Total expenses									28,521	26,519	15,691
Net income	$ 1,533	$ (70)	$ 1,305	$ 1,093	$ 1,610	$ 1,360	$ 726	$ 439	3,861	4,135	2,834
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest									4,718	4,556	908
Chubb limited (Parent Guarantor)
Condensed Financial Statements, Captions [Line Items]
Investment income, including intercompany interest income									336	356	35
Equity in net income of subsidiaries and affiliates									3,640	3,901	2,673
Net realized gains (losses)									0	0	0
Total revenues									3,976	4,257	2,708
Administrative and other (income) expense									63	39	(145)
Business Combination, Integration Related Costs									32	62	3
Income tax expense (benefit)									20	21	16
Total expenses									115	122	(126)
Net income									3,861	4,135	2,834
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest									$ 4,718	$ 4,556	$ 908