Summary of significant accounting policies (Narrative) (Detail) - USD ($) $ in Millions		6 Months Ended	12 Months Ended
		Dec. 31, 2022	Dec. 31, 2023		Dec. 31, 2022	Dec. 31, 2021	Jul. 01, 2023	Jul. 01, 2022	Jan. 01, 2021	Dec. 31, 2020
Summary of significant accounting policies [Line Items]
Deferred Policy Acquisition Costs, Amortization Expense			$ 8,259		$ 7,339	$ 6,758
Recoverable from unrated reinsurers, ceded reserve, default factor (percent)			34.00%
Percentage of fair value of loaned securities			102.00%
Quality assessment threshold used in goodwill impairment testing			50.00%
Property, Plant and Equipment, Net		$ 2,400	$ 2,900		2,400
Net operating results of ESIS included within Administrative expenses			(2)		12	25
Cigna integration expenses			69		48	0
Net income attributable to Chubb			9,028		5,246	8,525
Comprehensive Income (Loss), Net of Tax, Attributable to Parent			12,404		(3,865)	6,384
Retained earnings		48,305	54,810		48,305
Accumulated other comprehensive income		(10,185)	(6,809)		(10,185)
Stockholders' Equity		(50,519)	(59,507)		(50,519)	(58,328)
Reinsurance Recoverable for Paid and Unpaid Claims and Claims Adjustments	[1]	(18,859)	(19,952)		(18,859)
Reinsurance Recoverable Future Policy Benefits	[1]	(302)	(280)		(302)
Deferred policy acquisition costs		6,031	7,152		6,031
Value of business acquired		3,702	3,674		3,702	235				$ 263
Goodwill		16,228	19,686	[2]	16,228	15,213
Prepaid Reinsurance Premiums		(3,136)	(3,221)		(3,136)
Investments in partially-owned insurance companies		(2,507)	(191)		(2,507)
Liability for Claims and Claims Adjustment Expense		(75,747)	(80,122)		(75,747)	(72,330)				(67,192)
Unearned Premiums		(19,713)	(22,051)		(19,713)
Future policy benefits		10,476	13,888		10,476	7,837			$ 7,652
Market risk benefits		800	771		800
Reinsurance Payable		(7,780)	(8,302)		(7,780)
Deferred tax liabilities		377	1,555		377
Premiums Written, Net			(47,361)		(41,720)	(37,827)
Premiums Earned, Net			(45,712)		(40,360)	(36,292)
Realized Investment Gains (Losses)			607		1,085	(1,030)
Market Risk Benefit, Change in Fair Value, Gain (Loss)			307		(80)	(91)
Policyholder Benefits and Claims Incurred, Net			(24,100)		(22,572)	(21,030)
Liability for Future Policy Benefits, Period Expense (Income)			(3,628)		(2,314)	(1,740)
Other (income) expense			(836)		89	(2,367)
Income Tax Expense (Benefit)			(511)		(1,239)	(1,269)
Current discount rate on future policy benefits			84		1,480	387
Instrument-specific credit risk on market risk benefits			2		33	27
Other Comprehensive Income (Loss), Tax			(317)		965	366
Comprehensive income (loss)			12,376		(3,865)	6,384
Net Cash Provided by (Used in) Operating Activities, Total			12,632		11,258	11,151
Net Cash Provided by (Used in) Financing Activities			$ (4,489)		(5,142)	(4,411)
Huatai Group [Member]
Summary of significant accounting policies [Line Items]
Subsidiary, Ownership Percentage, Parent			76.50%				69.60%
Previously Reported
Summary of significant accounting policies [Line Items]
Deferred Policy Acquisition Costs, Amortization Expense					7,392	6,918
Net income attributable to Chubb					5,313	8,539
Comprehensive Income (Loss), Net of Tax, Attributable to Parent					(5,230)	6,020
Retained earnings		48,334			48,334
Accumulated other comprehensive income		(10,193)			(10,193)
Reinsurance Recoverable for Paid and Unpaid Claims and Claims Adjustments		(18,901)			(18,901)
Reinsurance Recoverable Future Policy Benefits		(303)			(303)
Deferred policy acquisition costs		5,788			5,788
Value of business acquired		3,596			3,596
Prepaid Reinsurance Premiums		(3,140)			(3,140)
Investments in partially-owned insurance companies		(2,877)			(2,877)
Liability for Claims and Claims Adjustment Expense		(76,323)			(76,323)
Unearned Premiums		(20,360)			(20,360)
Future policy benefits		10,120			10,120					$ 6,065	[3]
Market risk benefits		0			0
Reinsurance Payable		(7,795)			(7,795)
Deferred tax liabilities		292			292
Premiums Written, Net					(41,755)	(37,868)
Premiums Earned, Net					(40,389)	(36,355)
Realized Investment Gains (Losses)					965	(1,152)
Market Risk Benefit, Change in Fair Value, Gain (Loss)					0	0
Policyholder Benefits and Claims Incurred, Net					(23,342)	(21,980)
Liability for Future Policy Benefits, Period Expense (Income)					(1,492)	(699)
Other (income) expense					74	(2,365)
Income Tax Expense (Benefit)					(1,255)	(1,277)
Current discount rate on future policy benefits					0	0
Instrument-specific credit risk on market risk benefits					0	0
Other Comprehensive Income (Loss), Tax					(1,121)	(427)
Net Cash Provided by (Used in) Operating Activities, Total					11,243	11,149
Net Cash Provided by (Used in) Financing Activities					(5,127)	(4,409)
Effect of Modified Retrospective Application Accounting Standards Update 2018-12
Summary of significant accounting policies [Line Items]
Deferred Policy Acquisition Costs, Amortization Expense					53	160
Net income attributable to Chubb					67	14
Comprehensive Income (Loss), Net of Tax, Attributable to Parent					1,365	364
Retained earnings		29			29				52
Accumulated other comprehensive income		8			8				$ 1,800
Reinsurance Recoverable for Paid and Unpaid Claims and Claims Adjustments		(42)			(42)
Reinsurance Recoverable Future Policy Benefits		(1)			(1)
Deferred policy acquisition costs		243			243
Value of business acquired		106			106
Prepaid Reinsurance Premiums		(4)			(4)
Investments in partially-owned insurance companies		(370)			(370)
Liability for Claims and Claims Adjustment Expense		(576)			(576)
Unearned Premiums		(647)			(647)
Future policy benefits		356			356
Market risk benefits		800			800
Reinsurance Payable		(15)			(15)
Deferred tax liabilities		85			85
Premiums Written, Net					(35)	(41)
Premiums Earned, Net					(29)	(63)
Realized Investment Gains (Losses)					(120)	(122)
Market Risk Benefit, Change in Fair Value, Gain (Loss)					80	91
Policyholder Benefits and Claims Incurred, Net					(770)	(950)
Liability for Future Policy Benefits, Period Expense (Income)					822	1,041
Other (income) expense					15	(2)
Income Tax Expense (Benefit)					(16)	(8)
Current discount rate on future policy benefits					1,480	387
Instrument-specific credit risk on market risk benefits					33	27
Other Comprehensive Income (Loss), Tax					156	61
Net Cash Provided by (Used in) Operating Activities, Total					15	2
Net Cash Provided by (Used in) Financing Activities					(15)	$ (2)
Cigna's Life Insurance Business in Asian Markets
Summary of significant accounting policies [Line Items]
Net income attributable to Chubb		140
Stockholders' Equity								$ (5,380)
Reinsurance Recoverable for Paid and Unpaid Claims and Claims Adjustments								(3)
Reinsurance Recoverable Future Policy Benefits								(85)
Value of business acquired								3,633
Goodwill								1,189
Liability for Claims and Claims Adjustment Expense								(12)
Unearned Premiums								(61)
Future policy benefits								3,856
Reinsurance Payable								(115)
Deferred tax liabilities								$ 887
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		$ 74	$ 62		$ 74
Software Development [Member]
Summary of significant accounting policies [Line Items]
Property, Plant and Equipment, Net			$ 1,700
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			$ 510
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] At December 31, 2023, Goodwill from Huatai Group includes approximately $759 million attributable to noncontrolling interests

[3] Includes future policy benefits previously included within Unpaid losses and loss expenses on the pre-adoption Consolidated balance sheets, primarily certain international A&H business, and excludes deferred profit liability and certain guaranteed minimum death benefits reclassified to Market risk benefits on the post adoption period balance sheets.