Information Provided In Connection With Outstanding Debt Of Subsidiaries (Condensed Consolidating Statement Of Operations) (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Condensed Statement of Income Captions [Line Items]
Net premiums written	$ 7,902	$ 7,573	$ 22,193	$ 21,207
Net premiums earned	7,807	7,688	21,816	21,690
Net investment income	813	739	2,328	2,121
Equity in earnings of subsidiaries	0	0	0	0
Net realized gains (losses) including OTTI	(10)	100	84	(510)
Losses and loss expenses	6,247	4,269	14,182	12,197
Policy benefits	169	155	500	427
Policy acquisition costs and administrative expenses	2,202	2,286	6,430	6,860
Interest (income) expense	150	152	451	451
Other (income) expense	(118)	(91)	(333)	(92)
Amortization of purchased intangibles	65	4	194	16
Chubb integration expenses	50	115	233	361
Income tax benefit	(85)	277	243	556
Net income (loss)	(70)	1,360	2,328	2,525
Comprehensive income (loss)	629	1,376	3,711	4,457
Consolidating Adjustments and Eliminations
Condensed Statement of Income Captions [Line Items]
Net premiums written	0	0	0	0
Net premiums earned	0	0	0	0
Net investment income	0	0	0	0
Equity in earnings of subsidiaries	(85)	(2,040)	(3,731)	(4,134)
Net realized gains (losses) including OTTI	0	0	0	0
Losses and loss expenses	0	0	0	0
Policy benefits	0	0	0	0
Policy acquisition costs and administrative expenses	0	0	0	0
Interest (income) expense	0	0	0	0
Other (income) expense	0	0	0	0
Amortization of purchased intangibles	0	0	0	0
Chubb integration expenses	0	0	0	0
Income tax benefit	0	0	0	0
Net income (loss)	(85)	(2,040)	(3,731)	(4,134)
Comprehensive income (loss)	(1,472)	(2,066)	(6,477)	(7,528)
Chubb Limited (Parent Guarantor)
Condensed Statement of Income Captions [Line Items]
Net premiums written	0	0	0	0
Net premiums earned	0	0	0	0
Net investment income	1	1	3	3
Equity in earnings of subsidiaries	(127)	1,292	2,153	2,331
Net realized gains (losses) including OTTI	0	0	(2)	(1)
Losses and loss expenses	0	0	0	0
Policy benefits	0	0	0	0
Policy acquisition costs and administrative expenses	20	15	56	48
Interest (income) expense	(84)	(93)	(252)	(266)
Other (income) expense	(5)	(7)	(7)	(20)
Amortization of purchased intangibles	0	0	0	0
Chubb integration expenses	7	12	13	29
Income tax benefit	6	6	16	17
Net income (loss)	(70)	1,360	2,328	2,525
Comprehensive income (loss)	629	1,376	3,711	4,457
Chubb INA Holdings Inc (Subsidiary Issuer)
Condensed Statement of Income Captions [Line Items]
Net premiums written	0	0	0	0
Net premiums earned	0	0	0	0
Net investment income	3	2	10	9
Equity in earnings of subsidiaries	212	748	1,578	1,803
Net realized gains (losses) including OTTI	(8)	(2)	(22)	(3)
Losses and loss expenses	0	0	0	0
Policy benefits	0	0	0	0
Policy acquisition costs and administrative expenses	16	12	28	144
Interest (income) expense	208	233	641	681
Other (income) expense	9	6	34	26
Amortization of purchased intangibles	0	0	0	0
Chubb integration expenses	1	16	54	56
Income tax benefit	(89)	(136)	(288)	(323)
Net income (loss)	62	617	1,097	1,225
Comprehensive income (loss)	748	627	2,459	2,687
Other Chubb Limited Subsidiaries
Condensed Statement of Income Captions [Line Items]
Net premiums written	7,902	7,573	22,193	21,207
Net premiums earned	7,807	7,688	21,816	21,690
Net investment income	809	736	2,315	2,109
Equity in earnings of subsidiaries	0	0	0	0
Net realized gains (losses) including OTTI	(2)	102	108	(506)
Losses and loss expenses	6,247	4,269	14,182	12,197
Policy benefits	169	155	500	427
Policy acquisition costs and administrative expenses	2,166	2,259	6,346	6,668
Interest (income) expense	26	12	62	36
Other (income) expense	(122)	(90)	(360)	(98)
Amortization of purchased intangibles	65	4	194	16
Chubb integration expenses	42	87	166	276
Income tax benefit	(2)	407	515	862
Net income (loss)	23	1,423	2,634	2,909
Comprehensive income (loss)	$ 724	$ 1,439	$ 4,018	$ 4,841