Schedule II - Condensed Financial Information Of Registrant (Condensed Statements Of Operations) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Investment income, including intercompany interest income	$ 565	$ 564	$ 569	$ 544	$ 532	$ 516	$ 518	$ 504	$ 2,242	$ 2,070	$ 2,031
Net realized gains (losses)	83	(760)	(73)	(45)	305	(50)	9	168	(795)	432	(196)
Total revenues	4,479	4,294	4,253	3,808	4,409	3,888	3,760	3,949	16,834	16,006	15,075
Administrative and other (income) expense									2,052	1,858	1,811
Interest expense (benefit)									250	224	225
Total expenses									14,743	12,339	11,998
Net income	750	(31)	607	259	1,001	675	677	755	1,585	3,108	2,549
ACE Limited (Parent Guarantor) [Member]
Investment income, including intercompany interest income									39	38	44
Equity in net income of subsidiaries and affiliates									1,504	3,066	2,636
Net realized gains (losses)									(4)	(42)	(75)
Total revenues									1,539	3,062	2,605
Administrative and other (income) expense									(56)	(53)	61
Interest expense (benefit)									10	7	(5)
Total expenses									(46)	(46)	56
Net income									$ 1,585	$ 3,108	$ 2,549