Related party transaction (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Related Party Transaction [Line Items]
Net premiums written									$ 28,145	$ 17,713	$ 17,799
Losses and loss expenses	$ 3,855	$ 4,269	$ 4,254	$ 3,674	$ 2,302	$ 2,643	$ 2,417	$ 2,122	16,052	9,484	9,649
Insurance and reinsurance balances payable	5,637				4,270				5,637	4,270
Reinsurance recoverable on losses and loss expenses	13,577				11,386				13,577	11,386
Ceded Premiums Written									6,838	6,098	5,591
Starr Technical Risk Agency and Affiliates [Member]
Related Party Transaction [Line Items]
Paid commissions									145	60	63
Losses and loss expenses									313	137	91
Insurance and reinsurance balances payable	72				18				72	18
Reinsurance recoverable on losses and loss expenses	412				112				412	112
Gross premiums written									658	305	314
Ceded Premiums Written									208	78	84
Minimum Amount of Program Business to be Written to Earn Profit Sharing									20
Ceded Commissions									56	19	$ 20
Chubb Charitable Foundation Bermuda [Member]
Related Party Transaction [Line Items]
Chubb Charitable Foundation - Bermuda-Loan	23				24				23	24
ABR Reinsurance Capital Holdings Ltd. [Member]
Related Party Transaction [Line Items]
Insurance and reinsurance balances payable	53				6				53	6
Reinsurance recoverable on losses and loss expenses	$ 148				$ 82				148	82
Ceded Premiums Written									$ 288	$ 115
Equity Method Investment, Ownership Percentage					11.30%					11.30%