Schedule II - Condensed Financial Information Of Registrant (Condensed Statements Of Cash Flows) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Net cash flows from operating activities	$ 3,470	$ 3,546	$ 3,335
Purchases of fixed maturities available for sale	(23,823)	(29,985)	(31,789)
Sales of fixed maturities available for sale	17,176	23,096	23,693
Net derivative instruments settlements	(67)	(109)	(92)
Net cash flows from (used for) investing activities	(3,036)	(4,181)	(3,224)
Dividends paid on Common Shares	(459)	(435)	(388)
Net cash flows used for financing activities	(565)	732	(321)
Net increase (decrease) in cash	(158)	103	(198)
Cash - beginning of year	772	669	867
Cash - end of year	614	772	669
ACE Limited (Parent Guarantor) [Member]
Net cash flows from operating activities	762	(176)	594
Purchases of fixed maturities available for sale		(1)
Sales of fixed maturities available for sale	9		88
Net derivative instruments settlements	(3)	(3)
Capital contribution to subsidiaries	(385)	(290)	(90)
Advances (to) from affiliates	41	851	(174)
Other			(4)
Net cash flows from (used for) investing activities	(338)	557	(180)
Dividends paid on Common Shares	(459)	(435)	(388)
Net proceeds from issuance (repayment) of short-term debt	(300)	300
Proceeds from share-based compensation plans	133	63	25
Net cash flows used for financing activities	(626)	(72)	(363)
Net increase (decrease) in cash	(202)	309	51
Cash - beginning of year	308	(1)	(52)
Cash - end of year	$ 106	$ 308	$ (1)