Summary of significant accounting policies (Narrative) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Deposit Assets	$ 101	$ 107
Unpaid losses and loss expenses	72,943	67,811	$ 62,690	$ 62,960
Deposit liabilities included in Deposit liabilities	74	86
Borrowings under Guaranteed Investment Agreements	$ 2,200	2,200
Summary of significant accounting policies [Line Items]
Deferred Marketing Costs, Amortization Period	10 years
Deferred Advertising Costs	$ 189	226
Deferred Policy Acquisition Costs, Amortization Expense	$ 6,918	6,547	6,153
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	$ 2,000	2,000
Net operating results of ESIS included within Administrative expenses	25	18	47
Chubb integration expenses	0	0	23
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' Equity Attributable to Parent	(59,714)	(59,441)	(55,331)
The Chubb Corporation [Member] | Debt Securities [Member]
Summary of significant accounting policies [Line Items]
Assets, Fair Value Adjustment	127
Selling and Marketing Expense [Member]
Summary of significant accounting policies [Line Items]
Deferred Policy Acquisition Costs, Amortization Expense	85	99	109
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	90	110
Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' Equity Attributable to Parent	$ (47,365)	$ (39,337)	(36,142)	(31,700)
Minimum
Liability for Future Policy Benefit, by Product Segment [Line Items]
Liability for Future Policy Benefits, Interest Rate	1.00%	1.00%
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
Liability for Future Policy Benefit, by Product Segment [Line Items]
Liability for Future Policy Benefits, Interest Rate	9.00%	9.00%
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
Software Development [Member]
Summary of significant accounting policies [Line Items]
Property, Plant and Equipment, Net	$ 1,400
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	$ 228
Building [Member] | Maximum
Summary of significant accounting policies [Line Items]
Property, Plant and Equipment, Useful Life	40 years
Cumulative Effect, Period of Adoption, Adjustment [Member] | Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' Equity Attributable to Parent		$ 0	$ 72	$ 12