Summary of significant accounting policies (Narrative) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2016	Dec. 31, 2015		Dec. 31, 2014	Jan. 14, 2016	Dec. 31, 2013
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Business Combination, Integration Related Costs		$ 492	$ 33		$ 0
Affiliated notional cash pooling program	$ 300	300	0	[1]
Reinsurance business assumed		$ 20	21
Recoverable from unrated reinsurers, ceded reserve, default factor (percent)		34.00%
Debt Instrument [Line Items]
Unamortized Debt Issuance Expense			60
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Deposit assets reflected in Other assets	93	$ 93	86
Unpaid losses and loss expenses	60,540	60,540	37,303		38,315		$ 37,443
Deposit liabilities included in Deposit liabilities	108	108	110
Borrowings under Guaranteed Investment Agreements	1,500	1,500	1,100
Summary of significant accounting policies [Line Items]
Deferred Policy Acquisition Cost, Amortization Expense		5,904	2,941		3,075
Deferred Advertising Costs	256	$ 256	250
Deferred Marketing Costs, Amortization Period		10 years
Percentage of fair value of loaned securities		102.00%
Quality assessment threshold used in goodwill impairment testing		50.00%
Supplemental Information for Property, Casualty Insurance Underwriters, Reserves for Unpaid Claims and Claims Adjustment Expense	47,832	$ 47,832	26,562		27,008
Entity Well-known Seasoned Issuer		Yes
Net operating results of ESIS included within Administrative expenses		$ 32	30		27
Property, Plant and Equipment, Net	1,200	1,200	938
Finite-Lived Intangible Assets, Net	3,800	3,800	789
The Chubb Corporation [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Unpaid losses and loss expenses						$ 22,923
The Chubb Corporation [Member] | Debt Securities [Member]
Summary of significant accounting policies [Line Items]
Assets, Fair Value Adjustment	1,652	1,226
Selling and Marketing Expense [Member]
Summary of significant accounting policies [Line Items]
Deferred Policy Acquisition Cost, Amortization Expense		$ 92	$ 78		$ 99
Minimum
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest rates used in calculating future policy benefits		0.01	0.01
Summary of significant accounting policies [Line Items]
Reinsurance Premiums, Amortization Period		1 year
Amortization period for value of reinsurance business assumed		9 years
Finite-Lived Intangible Asset, Useful Life		1 year
Minimum | The Chubb Corporation [Member]
Summary of significant accounting policies [Line Items]
Amortization Period of Increase Decrease to Acquired Unpaid Losses and Loss Expenses		5 years
Maximum
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest rates used in calculating future policy benefits		0.080	0.072
Summary of significant accounting policies [Line Items]
Reinsurance Premiums, Amortization Period		3 years
Amortization period for value of reinsurance business assumed		40 years
Finite-Lived Intangible Asset, Useful Life		30 years
Maximum | The Chubb Corporation [Member]
Summary of significant accounting policies [Line Items]
Amortization Period of Increase Decrease to Acquired Unpaid Losses and Loss Expenses		17 years
Structured settlements
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Deposit assets reflected in Other assets	38	$ 38	$ 42
Unpaid losses and loss expenses	595	595
Reinsurance recoverables for amounts due from life insurance companies	557	557
Other Short-duration Insurance Product Line [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Unpaid losses and loss expenses	50	50	50
Long-term Debt [Member]
Debt Instrument [Line Items]
Unamortized Debt Issuance Expense			58
Trust Preferred Securities
Debt Instrument [Line Items]
Unamortized Debt Issuance Expense			$ 2
Fair Value Adjustment to Acquired Loss Reserves [Member] | The Chubb Corporation [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Increase Decrease on Acquired Unpaid Losses and Loss Expenses	$ 470	$ 470				$ 715
Fair Value Adjustment to Acquired Loss Reserves [Member] | Minimum | The Chubb Corporation [Member]
Summary of significant accounting policies [Line Items]
Finite-Lived Intangible Asset, Useful Life		5 years
Fair Value Adjustment to Acquired Loss Reserves [Member] | Maximum | The Chubb Corporation [Member]
Summary of significant accounting policies [Line Items]
Finite-Lived Intangible Asset, Useful Life		17 years

[1] Chubb maintains two notional multicurrency cash pools (Pools) with a third-party bank. Refer to Note 1 f) for additional information. At December 31, 2015, the cash balance of one or more entities was negative; however, the overall Pool balances were positive.