Information provided in connection with outstanding debt of subsidiaries (Condensed Consolidating Statement Of Operations and Comprehensive Income) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Information Provided In Connection With Outstanding Debt Of Subsidiaries [Line Items]
Net premiums written									$ 16,075		$ 15,372		$ 13,708
Net premiums earned	3,848	4,665	3,783	3,381	3,831	4,490	3,757	3,309	15,677		15,387		13,504
Net investment income	567	533	537	544	565	564	569	544	2,181		2,242		2,070
Equity in earnings of subsidiaries
Net realized gains (losses) including OTTI	272	(60)	(394)	260	83	(760)	(73)	(45)	78		(795)		432
Losses and loss expenses	2,683	3,047	2,119	1,804	2,286	2,745	2,226	2,263	9,653		9,520		7,579
Policy benefits	142	130	102	147	119	83	108	91	521		401		357
Policy acquisition costs and administrative expenses									4,542		4,540		4,218
Interest (income) expense									250		250		224
Other (income) expense									(6)		81		(10)
Income tax expense									270		502		553
Net income (loss)	765	640	328	973	735	(39)	594	250	2,706		1,540		3,085
Comprehensive income									3,682		1,857		3,856
ACE limited (Parent Gurantor)
Information Provided In Connection With Outstanding Debt Of Subsidiaries [Line Items]
Net premiums written
Net premiums earned
Net investment income									1		2		1
Equity in earnings of subsidiaries									2,590		1,459		3,043
Net realized gains (losses) including OTTI									17		(4)		(42)
Losses and loss expenses
Policy benefits
Policy acquisition costs and administrative expenses									62		69		70
Interest (income) expense									(33)		(37)		(37)
Other (income) expense									(137)		(125)		(123)
Income tax expense									10		10		7
Net income (loss)									2,706		1,540		3,085
Comprehensive income									3,682		1,857		3,856
ACE INA Holdings Inc. (Subsidiary Issuer)
Information Provided In Connection With Outstanding Debt Of Subsidiaries [Line Items]
Net premiums written													8,195
Net premiums earned													7,940
Net investment income													1,011
Equity in earnings of subsidiaries
Net realized gains (losses) including OTTI													303
Losses and loss expenses													4,910
Policy benefits													148
Policy acquisition costs and administrative expenses													2,395
Interest (income) expense													251
Other (income) expense													101
Income tax expense													441
Net income (loss)													1,008
Comprehensive income													1,271
Other ACE Limited Subsidiaries and Eliminations
Information Provided In Connection With Outstanding Debt Of Subsidiaries [Line Items]
Net premiums written													5,513	[1]
Net premiums earned													5,564	[1]
Net investment income													1,058	[1]
Equity in earnings of subsidiaries														[1]
Net realized gains (losses) including OTTI													171	[1]
Losses and loss expenses													2,669	[1]
Policy benefits													209	[1]
Policy acquisition costs and administrative expenses													1,753	[1]
Interest (income) expense													10	[1]
Other (income) expense													12	[1]
Income tax expense													105	[1]
Net income (loss)													2,035	[1]
Comprehensive income													1,772	[1]
Consolidating Adjustments
Information Provided In Connection With Outstanding Debt Of Subsidiaries [Line Items]
Net premiums written										[2]		[2]		[2]
Net premiums earned										[2]		[2]		[2]
Net investment income										[2]		[2]		[2]
Equity in earnings of subsidiaries									(2,590)	[2]	(1,459)	[2]	(3,043)	[2]
Net realized gains (losses) including OTTI										[2]		[2]		[2]
Losses and loss expenses										[2]		[2]		[2]
Policy benefits										[2]		[2]		[2]
Policy acquisition costs and administrative expenses										[2]		[2]		[2]
Interest (income) expense										[2]		[2]		[2]
Other (income) expense										[2]		[2]		[2]
Income tax expense										[2]		[2]		[2]
Net income (loss)									(2,590)	[2]	(1,459)	[2]	(3,043)	[2]
Comprehensive income									(2,590)	[2]	(1,459)	[2]	(3,043)	[2]
ACE INA Holdings Inc. (Subsidiary Issuer)
Information Provided In Connection With Outstanding Debt Of Subsidiaries [Line Items]
Net premiums written									9,466		9,081
Net premiums earned									9,194		9,082
Net investment income									1,048		1,096
Equity in earnings of subsidiaries
Net realized gains (losses) including OTTI									121		62
Losses and loss expenses									6,211		5,889
Policy benefits									309		192
Policy acquisition costs and administrative expenses									2,564		2,561
Interest (income) expense									257		267
Other (income) expense									77		143
Income tax expense									193		418
Net income (loss)									752		770
Comprehensive income									1,209		1,077
Other ACE Limited Subsidiaries and Eliminations
Information Provided In Connection With Outstanding Debt Of Subsidiaries [Line Items]
Net premiums written									6,609	[1]	6,291	[1]
Net premiums earned									6,483	[1]	6,305	[1]
Net investment income									1,132	[1]	1,144	[1]
Equity in earnings of subsidiaries										[1]		[1]
Net realized gains (losses) including OTTI									(60)	[1]	(853)	[1]
Losses and loss expenses									3,442	[1]	3,631	[1]
Policy benefits									212	[1]	209	[1]
Policy acquisition costs and administrative expenses									1,916	[1]	1,910	[1]
Interest (income) expense									26	[1]	20	[1]
Other (income) expense									54	[1]	63	[1]
Income tax expense									67	[1]	74	[1]
Net income (loss)									1,838	[1]	689	[1]
Comprehensive income									$ 1,381	[1]	$ 382	[1]

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

[2] Includes ACE Limited parent company eliminations.