Information Provided In Connection With Outstanding Debt Of Subsidiaries (Condensed Consolidating Statement Of Operations) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012		Jun. 30, 2013		Jun. 30, 2012
Information Provided In Connection With Outstanding Debt Of Subsidiaries [Line Items]
Net premiums written	$ 4,391		$ 4,130		$ 8,189		$ 7,702
Net premiums earned	4,067		3,783		7,640		7,164
Net investment income	534		537		1,065		1,081
Net realized gains (losses) including OTTI	104		(394)		310		(134)
Losses and loss expenses	2,250		2,119		4,176		3,923
Policy benefits	110		102		241		249
Policy acquisition costs and administrative expenses	1,229		1,133		2,357		2,225
Interest (income) expense	73		62		133		124
Other (income) expense	37		34		27		31
Income tax expense (benefit)	115		148		237		258
Net income (loss)	891		328		1,844		1,301
Comprehensive income (loss)	(499)		457		217		1,728
Parent Company [Member]
Information Provided In Connection With Outstanding Debt Of Subsidiaries [Line Items]
Net investment income	1		1		1		1
Equity in earnings of subsidiaries	842		301		1,756		1,229
Net realized gains (losses) including OTTI	0		2		12		22
Policy acquisition costs and administrative expenses	12		14		27		26
Interest (income) expense	(8)		(8)		(15)		(17)
Other (income) expense	(57)		(33)		(95)		(63)
Income tax expense (benefit)	5		3		8		5
Net income (loss)	891		328		1,844		1,301
Comprehensive income (loss)	(499)		457		217		1,728
Guarantor Subsidiaries [Member]
Information Provided In Connection With Outstanding Debt Of Subsidiaries [Line Items]
Net premiums written	2,502		2,327		4,584		4,425
Net premiums earned	2,331		2,196		4,337		4,148
Net investment income	254		257		502		522
Net realized gains (losses) including OTTI	28		34		38		60
Losses and loss expenses	1,434		1,325		2,687		2,507
Policy benefits	63		54		144		140
Policy acquisition costs and administrative expenses	674		656		1,300		1,296
Interest (income) expense	74		58		141		124
Other (income) expense	65		9		99		34
Income tax expense (benefit)	92		119		148		204
Net income (loss)	211		266		358		425
Comprehensive income (loss)	(533)		323		(534)		610
Other Ace Limited Subsidiaries And Eliminations [Member]
Information Provided In Connection With Outstanding Debt Of Subsidiaries [Line Items]
Net premiums written	1,889	[1]	1,803	[1]	3,605	[1]	3,277	[1]
Net premiums earned	1,736	[1]	1,587	[1]	3,303	[1]	3,016	[1]
Net investment income	279	[1]	279	[1]	562	[1]	558	[1]
Net realized gains (losses) including OTTI	76	[1]	(430)	[1]	260	[1]	(216)	[1]
Losses and loss expenses	816	[1]	794	[1]	1,489	[1]	1,416	[1]
Policy benefits	47	[1]	48	[1]	97	[1]	109	[1]
Policy acquisition costs and administrative expenses	543	[1]	463	[1]	1,030	[1]	903	[1]
Interest (income) expense	7	[1]	12	[1]	7	[1]	17	[1]
Other (income) expense	29	[1]	58	[1]	23	[1]	60	[1]
Income tax expense (benefit)	18	[1]	26	[1]	81	[1]	49	[1]
Net income (loss)	631	[1]	35	[1]	1,398	[1]	804	[1]
Comprehensive income (loss)	1,375	[1]	(22)	[1]	2,290	[1]	619	[1]
Consolidation, Eliminations [Member]
Information Provided In Connection With Outstanding Debt Of Subsidiaries [Line Items]
Equity in earnings of subsidiaries	(842)	[2]	(301)	[2]	(1,756)	[2]	(1,229)	[2]
Net income (loss)	(842)	[2]	(301)	[2]	(1,756)	[2]	(1,229)	[2]
Comprehensive income (loss)	$ (842)	[2]	$ (301)	[2]	$ (1,756)	[2]	$ (1,229)	[2]

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

[2] Includes ACE Limited parent company eliminations.