Summary of significant accounting policies (Narrative) (Detail) - USD ($) $ in Millions		6 Months Ended	12 Months Ended
		Dec. 31, 2022	Dec. 31, 2024		Dec. 31, 2023	Dec. 31, 2022	Jul. 01, 2023	Dec. 31, 2021
Summary of significant accounting policies [Line Items]
Deferred Policy Acquisition Costs, Amortization Expense			$ 9,102		$ 8,259	$ 7,339
Recoverable from unrated reinsurers, ceded reserve, default factor (percent)			11.20%
Percentage of fair value of loaned securities			102.00%
Quality assessment threshold used in goodwill impairment testing			50.00%
Property, Plant and Equipment, Net			$ 3,100		2,900
Net operating results of ESIS included within Administrative expenses			7		(2)	12
Integration expenses			39		69	48
Net income attributable to Chubb			9,272		9,028	5,246
Comprehensive Income (Loss), Net of Tax, Attributable to Parent			7,437		12,404	(3,865)
Retained earnings			61,561		54,810
Accumulated other comprehensive income (loss)			(8,644)		(6,809)
Stockholders' Equity		$ (50,519)	(64,021)		(59,507)	(50,519)
Reinsurance Recoverable for Paid and Unpaid Claims and Claims Adjustments	[1]		(19,777)		(19,952)
Reinsurance Recoverable Future Policy Benefits	[1]		(289)		(280)
Deferred policy acquisition costs			8,358		7,152
Value of business acquired		3,702	3,223		3,674	3,702		$ 235
Goodwill		16,228	19,579	[2]	19,686	16,228
Prepaid Reinsurance Premiums			(3,378)		(3,221)
Liability for Claims and Claims Adjustment Expense		(75,747)	(84,004)		(80,122)	(75,747)		$ (72,330)
Unearned Premiums			(23,504)		(22,051)
Future policy benefits			16,121		13,888
Market risk benefits			607		771
Reinsurance Payable			(8,121)		(8,302)
Deferred tax liabilities			1,584		1,555
Premiums Written, Net			(51,468)		(47,361)	(41,720)
Premiums Earned, Net			(49,846)		(45,712)	(40,360)
Realized Investment Gains (Losses)			(117)		607	1,085
Market Risk Benefit, Change in Fair Value, Gain (Loss)			140		307	(80)
Policyholder Benefits and Claims Incurred, Net			(26,022)		(24,100)	(22,572)
Liability for Future Policy Benefits, Period Expense (Income)			(4,714)		(3,628)	(2,314)
Other (income) expense			(1,023)		(836)	89
Income Tax Expense (Benefit)			(1,815)		(511)	(1,239)
Current discount rate on future policy benefits			(701)		84	1,480
Instrument-specific credit risk on market risk benefits			7		2	33
Other Comprehensive Income (Loss), Tax			(117)		(317)	965
Comprehensive income (loss)			7,658		12,376	(3,865)
Net Cash Provided by (Used in) Operating Activities, Total			16,182		12,632	11,258
Net Cash Provided by (Used in) Financing Activities			$ (2,181)		$ (4,489)	$ (5,142)
Huatai Group [Member]
Summary of significant accounting policies [Line Items]
Subsidiary, Ownership Percentage, Parent			85.50%		76.50%		69.60%
Cigna's Life Insurance Business in Asian Markets
Summary of significant accounting policies [Line Items]
Net income attributable to Chubb		$ 140
Minimum
Summary of significant accounting policies [Line Items]
Reinsurance Premiums, Amortization Period			1 year
Debt Securities, Held-to-Maturity, Accrued Interest, Threshold Period, Writeoff			30 days
Maximum
Summary of significant accounting policies [Line Items]
Reinsurance Premiums, Amortization Period			3 years
Affiliated notional cash pooling program			$ 300
Finite-Lived Intangible Asset, Useful Life			25 years
Debt Securities, Held-to-Maturity, Accrued Interest, Threshold Period, Writeoff			45 days
Fair Value Adjustment to Acquired Loss Reserves [Member] | The Chubb Corporation [Member]
Summary of significant accounting policies [Line Items]
Balance of FV adjustment on Unpaid Losses and Loss Expenses			$ 60		$ 62
Software Development [Member]
Summary of significant accounting policies [Line Items]
Property, Plant and Equipment, Net			$ 1,900
Property, Plant and Equipment, Useful Life			15 years
Software Development [Member] | Minimum
Summary of significant accounting policies [Line Items]
Property, Plant and Equipment, Useful Life			3 years
Software Development [Member] | Maximum
Summary of significant accounting policies [Line Items]
Property, Plant and Equipment, Useful Life			5 years
Building [Member]
Summary of significant accounting policies [Line Items]
Property, Plant and Equipment, Net			$ 431
Building [Member] | Maximum
Summary of significant accounting policies [Line Items]
Property, Plant and Equipment, Useful Life			40 years

[1] Net of valuation allowance for uncollectible reinsurance.

[2] Includes $499 million attributable to noncontrolling interests