Related party transaction (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Related Party Transaction [Line Items]
Document Period End Date									Dec. 31, 2015
Net premiums written									$ 17,713	$ 17,799	$ 17,025
Losses and loss expenses	$ 2,302	$ 2,643	$ 2,417	$ 2,122	$ 2,416	$ 2,684	$ 2,388	$ 2,161	9,484	9,649	9,348
Insurance and reinsurance balances payable	4,095								4,270	4,095
Reinsurance recoverable on losses and loss expenses	11,992								11,386	11,992
Ceded Premiums Written									6,098	5,591	5,803
Minimum Amount of Program Business to be Written to Earn Profit Sharing									20
Starr Technical Risk Agency and Affiliates [Member]
Related Party Transaction [Line Items]
Net commissions									41	43	42
Losses and loss expenses									137
Insurance and reinsurance balances payable	21								18	21
Reinsurance recoverable on losses and loss expenses	101								112	101
Gross premiums written									305	314	307
Ceded Premiums Written									78	84	$ 86
ACE Foundation Bermuda [Member]
Related Party Transaction [Line Items]
ACE Foundation - Bermuda-Loan	$ 25								$ 24	$ 25