Information Provided In Connection With Outstanding Debt Of Subsidiaries (Condensed Consolidating Balance Sheet) (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012		Dec. 31, 2011		Sep. 30, 2011		Dec. 31, 2010
Condensed Financial Statements, Captions [Line Items]
Investments	$ 59,817		$ 55,676
Cash	690	[1]	614		766	[2]	772	[2]
Insurance and reinsurance balances receivable	5,288		4,387
Reinsurance recoverable on losses and loss expenses	11,857		12,389
Reinsurance recoverable on policy benefits	246		249
Value of business acquired	632		676
Goodwill and other intangible assets	4,990		4,799
Other assets	9,988		8,531
Total assets	93,508		87,321
Unpaid losses and loss expenses	38,200		37,477
Unearned premiums	7,068		6,334
Future policy benefits	4,414		4,274
Short-term debt	1,402		1,251
Long-term debt	3,360		3,360
Trust preferred securities	309		309
Other liabilities	11,792		9,984
Total liabilities	66,545		62,989
Commitments and contingencies
Total shareholders' equity	26,963		24,332		23,581
Total liabilities and shareholders' equity	93,508		87,321
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Investments	31		33
Cash	(116)	[1]	106		(70)	[2]	308	[2]
Investments in subsidiaries	26,998		23,871
Due from subsidiaries and affiliates, net	270		498
Other assets	16		8
Total assets	27,199		24,516
Other liabilities	236		184
Total liabilities	236		184
Total shareholders' equity	26,963		24,332
Total liabilities and shareholders' equity	27,199		24,516
Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Investments	31,249		28,848
Cash	550	[1]	382		640	[2]	573	[2]
Insurance and reinsurance balances receivable	4,767		3,944
Reinsurance recoverable on losses and loss expenses	16,943		17,146
Reinsurance recoverable on policy benefits	1,196		941
Value of business acquired	628		676
Goodwill and other intangible assets	4,415		4,248
Other assets	7,711		7,018
Total assets	67,459		63,203
Unpaid losses and loss expenses	31,640		30,837
Unearned premiums	5,973		5,416
Future policy benefits	3,819		3,673
Due to subsidiaries and affiliates, net	584		316
Short-term debt	851		850
Long-term debt	3,360		3,360
Trust preferred securities	309		309
Other liabilities	8,992		7,769
Total liabilities	55,528		52,530
Total shareholders' equity	11,931		10,673
Total liabilities and shareholders' equity	67,459		63,203
Other ACE Limited Subsidiaries And Eliminations [Member]
Condensed Financial Statements, Captions [Line Items]
Investments	28,537	[3]	26,795	[3]
Cash	256	[1],[3]	126	[3]	196	[2],[3]	(109)	[2],[3]
Insurance and reinsurance balances receivable	521	[3]	443	[3]
Reinsurance recoverable on losses and loss expenses	(5,086)	[3]	(4,757)	[3]
Reinsurance recoverable on policy benefits	(950)	[3]	(692)	[3]
Value of business acquired	4
Goodwill and other intangible assets	575	[3]	551	[3]
Other assets	2,261	[3]	1,505	[3]
Total assets	26,118	[3]	23,971	[3]
Unpaid losses and loss expenses	6,560	[3]	6,640	[3]
Unearned premiums	1,095	[3]	918	[3]
Future policy benefits	595	[3]	601	[3]
Due to subsidiaries and affiliates, net	(314)	[3]	182	[3]
Short-term debt	551	[3]	401	[3]
Other liabilities	2,564	[3]	2,031	[3]
Total liabilities	11,051	[3]	10,773	[3]
Total shareholders' equity	15,067	[3]	13,198	[3]
Total liabilities and shareholders' equity	26,118		23,971	[3]
Consolidation, Eliminations [Member]
Condensed Financial Statements, Captions [Line Items]
Investments in subsidiaries	(26,998)	[4]	(23,871)	[4]
Due from subsidiaries and affiliates, net	(270)	[4]	(498)	[4]
Total assets	(27,268)	[4]	(24,369)	[4]
Due to subsidiaries and affiliates, net	(270)	[4]	(498)	[4]
Total liabilities	(270)	[4]	(498)	[4]
Total shareholders' equity	(26,998)	[4]	(23,871)	[4]
Total liabilities and shareholders' equity	$ (27,268)	[4]	$ (24,369)	[4]

[1] ACE maintains two notional multicurrency cash pools (Pools) with a third-party bank. Various ACE entities participate in one or the other of the Pools, pursuant to which credit and debit balances in individual ACE accounts are translated daily into a single currency and pooled on a notional basis. Individual ACE entities are permitted to overdraw on their individual accounts provided the overall Pool balances do not fall below zero. At September 30, 2012, the cash balance of one or more entities was negative; however, the overall Pool balances were positive.

[2] ACE maintains two notional multi-currency cash pools (Pools) with a third-party bank. Various ACE entities participate in one or the other of the Pools, pursuant to which credit and debit balances in individual ACE accounts are translated daily into a single currency and pooled on a notional basis. Individual ACE entities are permitted to overdraw on their individual accounts provided the overall Pool balances do not fall below zero. At September 30, 2011 and December 31, 2010, the cash balance of one or more entities was negative; however, the overall Pool balances were positive.

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

[4] Includes ACE Limited parent company eliminations.