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, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Condensed Statement of Income Captions [Line Items]
Net premiums written	$ 9,078	$ 8,622	$ 25,410	$ 24,278
Net premiums earned	8,765	8,327	24,687	23,355
Net investment income	840	873	2,528	2,568
Equity In Earnings Of Subsidiaries	0	0	0	0
Net Realized Gains Losses	(141)	(155)	(1,069)	(475)
Net gains (losses) recognized during the period	(141)	(155)	(1,069)	(475)
Losses and loss expenses	5,835	5,052	16,897	13,865
Policy benefits	198	158	550	515
Policy acquisition costs and administrative expenses	2,378	2,355	7,054	6,831
Interest (income) expense	130	138	390	418
Other (income) expense	(485)	(57)	(372)	(326)
Amortization of purchased intangibles	72	76	217	229
Chubb integration expenses	0	2	0	9
Income tax expense	142	230	295	626
Net income	1,194	1,091	1,115	3,281
Comprehensive income (loss)	1,952	1,473	2,352	6,250
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	0	1	(2)	3
Equity In Earnings Of Subsidiaries	1,174	1,053	1,064	3,147
Net gains (losses) recognized during the period	3	(4)	5	1
Losses and loss expenses	0	0	0	0
Policy benefits	0	0	0	0
Policy acquisition costs and administrative expenses	21	22	66	64
Interest (income) expense	(34)	(59)	(103)	(187)
Other (income) expense	(10)	(7)	(27)	(19)
Amortization of purchased intangibles	0	0	0	0
Chubb integration expenses		0		0
Income tax expense	6	3	16	12
Net income	1,194	1,091	1,115	3,281
Comprehensive income (loss)	1,952	1,473	2,352	6,250
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	1	(3)	6	(13)
Equity In Earnings Of Subsidiaries	516	824	838	2,345
Net gains (losses) recognized during the period	(192)	68	(271)	34
Losses and loss expenses	0	0	0	0
Policy benefits	0	0	0	0
Policy acquisition costs and administrative expenses	(33)	(5)	(101)	(25)
Interest (income) expense	151	171	448	536
Other (income) expense	(2)	(3)	1	1
Amortization of purchased intangibles	0	0	0	0
Chubb integration expenses		0		2
Income tax expense	(66)	(33)	(125)	(120)
Net income	275	759	350	1,972
Comprehensive income (loss)	812	1,138	1,484	4,476
Other Chubb Limited Subsidiaries
Condensed Statement of Income Captions [Line Items]
Net premiums written	9,078	8,622	25,410	24,278
Net premiums earned	8,765	8,327	24,687	23,355
Net investment income	839	875	2,524	2,578
Equity In Earnings Of Subsidiaries	0	0	0	0
Net gains (losses) recognized during the period	48	(219)	(803)	(510)
Losses and loss expenses	5,835	5,052	16,897	13,865
Policy benefits	198	158	550	515
Policy acquisition costs and administrative expenses	2,390	2,338	7,089	6,792
Interest (income) expense	13	26	45	69
Other (income) expense	(473)	(47)	(346)	(308)
Amortization of purchased intangibles	72	76	217	229
Chubb integration expenses		2		7
Income tax expense	202	260	404	734
Net income	1,415	1,118	1,552	3,520
Comprehensive income (loss)	2,180	1,517	2,840	6,486
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	(1,690)	(1,877)	(1,902)	(5,492)
Net gains (losses) recognized during the period	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
Income tax expense	0	0	0	0
Net income	(1,690)	(1,877)	(1,902)	(5,492)
Comprehensive income (loss)	$ (2,992)	$ (2,655)	$ (4,324)	$ (10,962)