Information Provided In Connection With Outstanding Debt Of Subsidiaries (Condensed Consolidating Statement Of Operations) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012
Information Provided In Connection With Outstanding Debt Of Subsidiaries [Line Items]
Net premiums written	$ 3,798		$ 3,572
Net premiums earned	3,573		3,381
Net investment income	531		544
Net realized gains (losses) including OTTI	206		260
Losses and loss expenses	1,926		1,804
Policy benefits	131		147
Policy acquisition costs and administrative expenses	1,128		1,092
Interest (income) expense	60		62
Other (income) expense	(10)		(3)
Income tax expense (benefit)	122		110
Net income (loss)	953		973
Comprehensive income	716		1,271
Parent Company [Member]
Information Provided In Connection With Outstanding Debt Of Subsidiaries [Line Items]
Net investment income	0
Equity in earnings of subsidiaries	914		928
Net realized gains (losses) including OTTI	12		20
Policy acquisition costs and administrative expenses	15		12
Interest (income) expense	(7)		(9)
Other (income) expense	(38)		(30)
Income tax expense (benefit)	3		2
Net income (loss)	953		973
Comprehensive income	716		1,271
Guarantor Subsidiaries [Member]
Information Provided In Connection With Outstanding Debt Of Subsidiaries [Line Items]
Net premiums written	2,082		2,098
Net premiums earned	2,006		1,952
Net investment income	248		265
Net realized gains (losses) including OTTI	10		26
Losses and loss expenses	1,253		1,182
Policy benefits	81		86
Policy acquisition costs and administrative expenses	626		640
Interest (income) expense	67		66
Other (income) expense	34		25
Income tax expense (benefit)	56		85
Net income (loss)	147		159
Comprehensive income	(1)		287
Other ACE Limited Subsidiaries And Eliminations [Member]
Information Provided In Connection With Outstanding Debt Of Subsidiaries [Line Items]
Net premiums written	1,716	[1]	1,474	[1]
Net premiums earned	1,567	[1]	1,429	[1]
Net investment income	283	[1]	279	[1]
Net realized gains (losses) including OTTI	184	[1]	214	[1]
Losses and loss expenses	673	[1]	622	[1]
Policy benefits	50	[1]	61	[1]
Policy acquisition costs and administrative expenses	487	[1]	440	[1]
Interest (income) expense	0	[1]	5	[1]
Other (income) expense	(6)	[1]	2	[1]
Income tax expense (benefit)	63	[1]	23	[1]
Net income (loss)	767	[1]	769	[1]
Comprehensive income	915	[1]	641	[1]
Consolidation, Eliminations [Member]
Information Provided In Connection With Outstanding Debt Of Subsidiaries [Line Items]
Equity in earnings of subsidiaries	(914)	[2]	(928)	[2]
Net income (loss)	(914)	[2]	(928)	[2]
Comprehensive income	$ (914)	[2]	$ (928)	[2]

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

[2] Includes ACE Limited parent company eliminations.