Information Provided In Connection With Outstanding Debt Of Subsidiaries (Condensed Consolidating Statement Of Operations) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012		Mar. 31, 2011
Information Provided In Connection With Outstanding Debt Of Subsidiaries [Line Items]
Net premiums written	$ 3,572		$ 3,446
Net premiums earned	3,381		3,309
Net investment income	544		544
Net realized gains (losses) including OTTI	260		(45)
Losses and loss expenses	1,804		2,263
Policy benefits	147		91
Policy acquisition costs and administrative expenses	1,092		1,058
Interest (income) expense	62		63
Other (income) expense	(3)		(13)
Income tax expense	110		96
Net income (loss)	973		250
Comprehensive income	1,271		438
ACE Limited (Parent Guarantor) [Member]
Information Provided In Connection With Outstanding Debt Of Subsidiaries [Line Items]
Net investment income			1
Equity in earnings of subsidiaries	928		239
Net realized gains (losses) including OTTI	20		(1)
Policy acquisition costs and administrative expenses	12		18
Interest (income) expense	(9)		(8)
Other (income) expense	(30)		(22)
Income tax expense	2		1
Net income (loss)	973		250
Comprehensive income	1,271		438
ACE INA Holdings Inc. (Subsidiary Issuer) [Member]
Information Provided In Connection With Outstanding Debt Of Subsidiaries [Line Items]
Net premiums written	2,098		2,023
Net premiums earned	1,952		1,938
Net investment income	265		262
Net realized gains (losses) including OTTI	26		(13)
Losses and loss expenses	1,182		1,301
Policy benefits	86		40
Policy acquisition costs and administrative expenses	640		588
Interest (income) expense	66		67
Other (income) expense	25		13
Income tax expense	85		68
Net income (loss)	159		110
Comprehensive income	287		210
Other ACE Limited Subsidiaries And Eliminations [Member]
Information Provided In Connection With Outstanding Debt Of Subsidiaries [Line Items]
Net premiums written	1,474	[1]	1,423	[1]
Net premiums earned	1,429	[1]	1,371	[1]
Net investment income	279	[1]	281	[1]
Net realized gains (losses) including OTTI	214	[1]	(31)	[1]
Losses and loss expenses	622	[1]	962	[1]
Policy benefits	61	[1]	51	[1]
Policy acquisition costs and administrative expenses	440	[1]	452	[1]
Interest (income) expense	5	[1]	4	[1]
Other (income) expense	2	[1]	(4)	[1]
Income tax expense	23	[1]	27	[1]
Net income (loss)	769	[1]	129	[1]
Comprehensive income	641	[1]	29	[1]
Consolidating Adjustments [Member]
Information Provided In Connection With Outstanding Debt Of Subsidiaries [Line Items]
Equity in earnings of subsidiaries	(928)	[2]	(239)	[2]
Net income (loss)	(928)	[2]	(239)	[2]
Comprehensive income	$ (928)	[2]	$ (239)	[2]

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

[2] Includes ACE Limited parent company eliminations.