Information Provided In Connection With Outstanding Debt Of Subsidiaries (Condensed Consolidating Statement 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
Information Provided In Connection With Outstanding Debt Of Subsidiaries [Line Items]
Net premiums written									$ 15,372		$ 13,708		$ 13,299
Net premiums earned	3,831	4,490	3,757	3,309	3,572	3,422	3,233	3,277	15,387		13,504		13,240
Net investment income	565	564	569	544	532	516	518	504	2,242		2,070		2,031
Net realized gains (losses) including OTTI	83	(760)	(73)	(45)	305	(50)	9	168	(795)		432		(196)
Losses and loss expenses	2,286	2,745	2,226	2,263	1,971	1,887	1,800	1,921	9,520		7,579		7,422
Policy benefits	119	83	108	91	90	93	87	87	401		357		325
Interest (income) expense									250		224		225
Other (income) expense									73		(16)		85
Income tax expense (benefit)									506		559		528
Net income	750	(31)	607	259	1,001	675	677	755	1,585		3,108		2,549
ACE Limited (Parent Guarantor) [Member]
Information Provided In Connection With Outstanding Debt Of Subsidiaries [Line Items]
Net investment income									2		1		1
Equity in earnings of subsidiaries									1,504		3,066		2,636
Net realized gains (losses) including OTTI									(4)		(42)		(75)
Policy acquisition costs and administrative expenses									69		70		54
Interest (income) expense													(43)
Interest (income) expense									(37)		(37)
Other (income) expense									(125)		(123)		7
Income tax expense (benefit)									10		7		(5)
Net income									1,585		3,108		2,549
ACE INA Holdings Inc. (Subsidiary Issuer) [Member]
Information Provided In Connection With Outstanding Debt Of Subsidiaries [Line Items]
Net premiums written									9,081		8,195		7,407
Net premiums earned									9,082		7,940		7,411
Net investment income									1,096		1,011		1,003
Net realized gains (losses) including OTTI									62		303		75
Losses and loss expenses									5,889		4,910		4,620
Policy benefits									192		148		84
Policy acquisition costs and administrative expenses									2,520		2,372		2,180
Interest (income) expense													261
Interest (income) expense									267		251
Other (income) expense									135		95		44
Income tax expense (benefit)									422		447		395
Net income									815		1,031		905
Other ACE Limited Subsidiaries And Eliminations [Member]
Information Provided In Connection With Outstanding Debt Of Subsidiaries [Line Items]
Net premiums written									6,291	[1]	5,513	[1]	5,892	[1]
Net premiums earned									6,305	[1]	5,564	[1]	5,829	[1]
Net investment income									1,144	[1]	1,058	[1]	1,027	[1]
Net realized gains (losses) including OTTI									(853)	[1]	171	[1]	(196)	[1]
Losses and loss expenses									3,631	[1]	2,669	[1]	2,802	[1]
Policy benefits									209	[1]	209	[1]	241	[1]
Policy acquisition costs and administrative expenses									1,910	[1]	1,753	[1]	1,707	[1]
Interest (income) expense													7	[1]
Interest (income) expense									20	[1]	10	[1]
Other (income) expense									63	[1]	12	[1]	34	[1]
Income tax expense (benefit)									74	[1]	105	[1]	138	[1]
Net income									689	[1]	2,035	[1]	1,731	[1]
Consolidating Adjustments [Member]
Information Provided In Connection With Outstanding Debt Of Subsidiaries [Line Items]
Equity in earnings of subsidiaries									(1,504)	[2]	(3,066)	[2]	(2,636)	[2]
Net income									(1,504)	[2]	(3,066)	[2]	(2,636)	[2]
ACE Limited Consolidated [Member]
Information Provided In Connection With Outstanding Debt Of Subsidiaries [Line Items]
Net premiums written									15,372		13,708		13,299
Net premiums earned									15,387		13,504		13,240
Net investment income									2,242		2,070		2,031
Net realized gains (losses) including OTTI									(795)		432		(196)
Losses and loss expenses									9,520		7,579		7,422
Policy benefits									401		357		325
Policy acquisition costs and administrative expenses									4,499		4,195		3,941
Interest (income) expense													225
Interest (income) expense									250		224
Other (income) expense									73		(16)		85
Income tax expense (benefit)									506		559		528
Net income									$ 1,585		$ 3,108		$ 2,549

[1] Includes all other subsidiaries of ACE Limited and intercompany eliminations.

[2] Includes ACE Limited parent company eliminations.