Summary of significant accounting policies (Narrative) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Summary of significant accounting policies [Line Items]
Deferred Marketing Costs, Amortization Period	10 years
Deferred marketing costs reported in Deferred policy acquisition costs	$ 250	$ 288
Amortization expense for deferred marketing costs	$ 78	99	$ 128
Recoverable from unrated reinsurers, ceded reserve, default factor (percent)	34.00%
Reinsurance business assumed	$ 21	26
Percentage of fair value of loaned securities	102.00%
Maximum overdraft balance guaranteed by ACE Ltd	$ 300
Quality assessment threshold used in goodwill impairment testing	50.00%
Unpaid losses and loss expenses	$ 37,303	38,315	37,443	$ 37,946
Supplemental Information for Property, Casualty Insurance Underwriters, Reserves for Unpaid Claims and Claims Adjustment Expense	26,562	27,008	26,831
Gross liability for the amounts due to claimants	588
Reinsurance recoverables for amounts due from life insurance companies	546
Deposit assets reflected in Other assets	86	89
Reinsurance deposit liabilities included in Deposit liabilities	110	120
Contract holder deposit funds included in Deposit liabilities	1,100	908
Net operating results of ESIS included within Administrative expenses	30	27	$ 25
Structured settlements
Summary of significant accounting policies [Line Items]
Unpaid losses and loss expenses	42	49
Discounted Unsettled Claims [Member]
Summary of significant accounting policies [Line Items]
Unpaid losses and loss expenses	$ 50	$ 62
Minimum
Summary of significant accounting policies [Line Items]
Amortization period for value of reinsurance business assumed	9 years
Finite-lived intangible asset useful life	1 year
Interest rates used in calculating reserves	1.00%	1.00%
Reinsurance Premiums, Amortization Period	1 year
Maximum
Summary of significant accounting policies [Line Items]
Amortization period for value of reinsurance business assumed	40 years
Finite-lived intangible asset useful life	30 years
Interest rates used in calculating reserves	7.20%	6.50%
Reinsurance Premiums, Amortization Period	3 years