Information provided in connection with outstanding debt of subsidiaries (Condensed Consolidating Statement Of Operations and Comprehensive Income) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Information Provided In Connection With Outstanding Debt Of Subsidiaries [Line Items]
Net premiums written	$ 33,820	$ 32,275	$ 30,579
Net premiums earned	33,117	31,290	30,064
Net Investment Income	3,375	3,426	3,305
Equity in earnings of subsidiaries	0	0	0
Realized Investment Gains (Losses)	(498)	(530)	(652)
Losses and loss expenses	21,710	18,730	18,067
Policy benefits	784	740	590
Policy acquisition costs and administrative expenses	9,526	9,183	8,798
Interest (income) expense	516	552	641
Other (Income) Expense	(994)	(596)	(434)
Amortization of Purchased Intangibles	290	305	339
Chubb integration expenses	0	23	59
Income tax expense (benefit)	629	795	695
Net income	3,533	4,454	3,962
Comprehensive income	5,783	7,521	1,242
Chubb limited (Parent Guarantor)
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	(1)	1	6
Equity in earnings of subsidiaries	3,457	4,307	3,753
Realized Investment Gains (Losses)	20	(17)	0
Losses and loss expenses	0	0	0
Policy benefits	0	0	0
Policy acquisition costs and administrative expenses	94	92	87
Interest (income) expense	(136)	(243)	(299)
Other (Income) Expense	(39)	(27)	(24)
Amortization of Purchased Intangibles	0	0	0
Chubb integration expenses	0	1	14
Income tax expense (benefit)	24	14	19
Net income	3,533	4,454	3,962
Comprehensive income	5,783	7,521	1,242
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	6	(15)	13
Equity in earnings of subsidiaries	2,052	3,022	2,578
Realized Investment Gains (Losses)	(397)	(31)	117
Losses and loss expenses	0	0	0
Policy benefits	0	0	0
Policy acquisition costs and administrative expenses	(130)	(26)	(58)
Interest (income) expense	596	705	806
Other (Income) Expense	(24)	6	26
Amortization of Purchased Intangibles	0	0	0
Chubb integration expenses		2	1
Income tax expense (benefit)	(181)	(175)	(148)
Net income	1,400	2,464	2,081
Comprehensive income	3,236	4,988	(27)
Other Chubb Limited Subsidiaries and Eliminations
Information Provided In Connection With Outstanding Debt Of Subsidiaries [Line Items]
Net premiums written	33,820	32,275	30,579
Net premiums earned	33,117	31,290	30,064
Net Investment Income	3,370	3,440	3,286
Equity in earnings of subsidiaries	0	0	0
Realized Investment Gains (Losses)	(121)	(482)	(769)
Losses and loss expenses	21,710	18,730	18,067
Policy benefits	784	740	590
Policy acquisition costs and administrative expenses	9,562	9,117	8,769
Interest (income) expense	56	90	134
Other (Income) Expense	(931)	(575)	(436)
Amortization of Purchased Intangibles	290	305	339
Chubb integration expenses		20	44
Income tax expense (benefit)	786	956	824
Net income	4,109	4,865	4,250
Comprehensive income	6,512	7,922	1,808
Consolidating Adjustments
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	0	0	0
Equity in earnings of subsidiaries	(5,509)	(7,329)	(6,331)
Realized Investment Gains (Losses)	0	0	0
Losses and loss expenses	0	0	0
Policy benefits	0	0	0
Policy acquisition costs and administrative expenses	0	0	0
Interest (income) expense	0	0	0
Other (Income) Expense	0	0	0
Amortization of Purchased Intangibles	0	0	0
Chubb integration expenses		0	0
Income tax expense (benefit)	0	0	0
Net income	(5,509)	(7,329)	(6,331)
Comprehensive income	$ (9,748)	$ (12,910)	$ (1,781)