Information provided in connection with outstanding debt of subsidiaries (Condensed Consolidating Statement Of Cash Flows) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Information Provided In Connection With Outstanding Debt Of Subsidiaries [Line Items]
Net cash flows from operating activities	$ 3,995		$ 3,470		$ 3,546
Purchases of fixed maturities available for sale	(23,844)		(24,578)		(31,256)
Purchases of fixed maturities held to maturity	(388)		(340)		(616)
Purchases of equity securities	(135)		(309)		(794)
Sales of fixed maturities available for sale	14,769		17,971		24,279
Sales of equity securities	119		376		774
Maturities and redemptions of fixed maturities available for sale	5,523		3,720		3,660
Maturities and redemptions of fixed maturities held to maturity	1,451		1,279		1,353
Net derivative instruments settlements	(281)		(67)		(109)
Advances from (to) affiliates
Acquisition of subsidiaries (net of cash acquired of $8, $91 and $80)	(98)		(606)		(1,139)
Capital contribution to subsidiary
Other	(555)		(482)		(333)
Net cash flows from (used for) investing activities	(3,439)		(3,036)		(4,181)
Dividends paid on Common Shares	(815)		(459)		(435)
Common Shares repurchased	(11)		(195)		(235)
Net proceeds from (repayments) issuance of short-term debt	150		(50)		1,141
Net proceeds from issuances of long-term debt					199
Proceeds from share-based compensation plans	126		139		62
Advances from (to) affiliates
Capital contribution from subsidiary
Dividends to parent company
Cash contributions from parent
Net cash flows from (used for) financing activities	(550)		(565)		732
Effect of foreign currency rate changes on cash and cash equivalents	(5)		(27)		6
Net increase (decrease) in cash	1		(158)		103
Cash - beginning of period	614		772	[1],[2]	669	[1]
Cash - end of period	615	[3],[4]	614		772	[1],[2]
ACE limited (Parent Gurantor)
Information Provided In Connection With Outstanding Debt Of Subsidiaries [Line Items]
Net cash flows from operating activities	781		762		(176)
Purchases of fixed maturities available for sale					(1)
Purchases of fixed maturities held to maturity
Purchases of equity securities
Sales of fixed maturities available for sale			9
Sales of equity securities
Maturities and redemptions of fixed maturities available for sale
Maturities and redemptions of fixed maturities held to maturity
Net derivative instruments settlements	(1)		(3)		(3)
Advances from (to) affiliates	(2)		41		851
Acquisition of subsidiaries (net of cash acquired of $8, $91 and $80)
Capital contribution to subsidiary			(385)		(290)
Other
Net cash flows from (used for) investing activities	(3)		(338)		557
Dividends paid on Common Shares	(815)		(459)		(435)
Common Shares repurchased
Net proceeds from (repayments) issuance of short-term debt			(300)		300
Net proceeds from issuances of long-term debt					0
Proceeds from share-based compensation plans	34		133		63
Advances from (to) affiliates
Capital contribution from subsidiary
Dividends to parent company
Cash contributions from parent
Net cash flows from (used for) financing activities	(781)		(626)		(72)
Effect of foreign currency rate changes on cash and cash equivalents
Net increase (decrease) in cash	(3)		(202)		309
Cash - beginning of period	106		308	[2]	(1)	[1]
Cash - end of period	103	[3],[4]	106		308	[2]
ACE INA Holdings Inc. (Subsidiary Issuer)
Information Provided In Connection With Outstanding Debt Of Subsidiaries [Line Items]
Net cash flows from operating activities	1,744		1,053		1,798
Purchases of fixed maturities available for sale	(11,843)		(12,203)		(13,785)
Purchases of fixed maturities held to maturity	(384)		(338)		(615)
Purchases of equity securities	(70)		(157)		(107)
Sales of fixed maturities available for sale	7,347		9,718		10,225
Sales of equity securities	59		354		17
Maturities and redemptions of fixed maturities available for sale	2,759		1,784		1,845
Maturities and redemptions of fixed maturities held to maturity	1,045		933		1,142
Net derivative instruments settlements	(6)		(24)		(10)
Advances from (to) affiliates
Acquisition of subsidiaries (net of cash acquired of $8, $91 and $80)	(111)		(569)		(1,139)
Capital contribution to subsidiary
Other	(395)		(420)		(253)
Net cash flows from (used for) investing activities	(1,599)		(922)		(2,680)
Dividends paid on Common Shares
Common Shares repurchased
Net proceeds from (repayments) issuance of short-term debt	1		(150)		841
Net proceeds from issuances of long-term debt					199
Proceeds from share-based compensation plans	13		3		0
Advances from (to) affiliates	(105)		(149)		3
Capital contribution from subsidiary	90
Dividends to parent company	0		0
Cash contributions from parent
Net cash flows from (used for) financing activities	(1)		(296)		1,043
Effect of foreign currency rate changes on cash and cash equivalents	(11)		(26)		12
Net increase (decrease) in cash	133		(191)		173
Cash - beginning of period	382		573	[2]	400	[1]
Cash - end of period	515	[3],[4]	382		573	[2]
Other ACE Limited Subsidiaries and Eliminations
Information Provided In Connection With Outstanding Debt Of Subsidiaries [Line Items]
Net cash flows from operating activities	1,920	[5]	2,395	[5]	2,124	[5]
Purchases of fixed maturities available for sale	(12,001)	[5]	(12,375)	[5]	(17,470)	[5]
Purchases of fixed maturities held to maturity	(4)	[5]	(2)	[5]	(1)	[5]
Purchases of equity securities	(65)	[5]	(152)	[5]	(687)	[5]
Sales of fixed maturities available for sale	7,422	[5]	8,244	[5]	14,054	[5]
Sales of equity securities	60	[5]	22	[5]	757	[5]
Maturities and redemptions of fixed maturities available for sale	2,764	[5]	1,936	[5]	1,815	[5]
Maturities and redemptions of fixed maturities held to maturity	406	[5]	346	[5]	211	[5]
Net derivative instruments settlements	(274)	[5]	(40)	[5]	(96)	[5]
Advances from (to) affiliates		[5]		[5]		[5]
Acquisition of subsidiaries (net of cash acquired of $8, $91 and $80)	13	[5]	(37)	[5]		[5]
Capital contribution to subsidiary	(90)	[5]		[5]		[5]
Other	(160)	[5]	(62)	[5]	(80)	[5]
Net cash flows from (used for) investing activities	(1,929)	[5]	(2,120)	[5]	(1,497)
Dividends paid on Common Shares		[5]		[5]		[5]
Common Shares repurchased	(11)	[5]	(195)	[5]	(235)	[5]
Net proceeds from (repayments) issuance of short-term debt	149	[5]	400	[5]		[5]
Net proceeds from issuances of long-term debt					0
Proceeds from share-based compensation plans	79	[5]	3	[5]	(1)
Advances from (to) affiliates	107	[5]	108	[5]	(854)	[5]
Capital contribution from subsidiary		[5]
Dividends to parent company	(450)	[5]	(740)	[5]	(200)	[5]
Cash contributions from parent			385	[5]	290	[5]
Net cash flows from (used for) financing activities	(126)	[5]	(39)	[5]	(1,000)
Effect of foreign currency rate changes on cash and cash equivalents	6	[5]	(1)	[5]	(6)	[5]
Net increase (decrease) in cash	(129)	[5]	235	[5]	(379)
Cash - beginning of period	126	[5]	(109)	[2],[5]	270	[1],[5]
Cash - end of period	(3)	[3],[4],[5]	126	[5]	(109)	[2],[5]
Consolidating Adjustments
Information Provided In Connection With Outstanding Debt Of Subsidiaries [Line Items]
Net cash flows from operating activities	(450)	[6]	(740)	[6]	(200)	[1]
Purchases of fixed maturities available for sale		[6]		[6]		[1]
Purchases of fixed maturities held to maturity		[6]		[6]		[1]
Purchases of equity securities		[6]		[6]		[1]
Sales of fixed maturities available for sale		[6]		[6]		[1]
Sales of equity securities		[6]		[6]		[1]
Maturities and redemptions of fixed maturities available for sale		[6]		[6]		[1]
Maturities and redemptions of fixed maturities held to maturity		[6]		[6]		[1]
Net derivative instruments settlements		[6]		[6]		[1]
Advances from (to) affiliates	2	[6]	(41)	[6]	(851)	[1]
Acquisition of subsidiaries (net of cash acquired of $8, $91 and $80)		[6]		[6]		[1]
Capital contribution to subsidiary	90	[6]	385	[6]	290	[1]
Other		[6]		[6]		[1]
Net cash flows from (used for) investing activities	92	[6]	344	[6]	(561)
Dividends paid on Common Shares		[6]		[6]		[1]
Common Shares repurchased		[6]		[6]		[1]
Net proceeds from (repayments) issuance of short-term debt		[6]		[6]		[1]
Net proceeds from issuances of long-term debt					0
Proceeds from share-based compensation plans		[6]			0
Advances from (to) affiliates	(2)	[6]	41	[6]	851	[1]
Capital contribution from subsidiary	(90)	[6]
Dividends to parent company	450	[6]	740	[6]	200	[1]
Cash contributions from parent			(385)	[6]	(290)	[1]
Net cash flows from (used for) financing activities	358	[6]	396	[6]	761
Effect of foreign currency rate changes on cash and cash equivalents		[6]		[6]		[1]
Net increase (decrease) in cash		[6]		[6]	0
Cash - beginning of period		[6],[7]	0	[2],[6]		[1]
Cash - end of period		[3],[4],[6],[7]		[6],[7]	$ 0	[2],[6]

[1] ACE maintains two notional multi-currency cash pools (Pools) with a third-party bank. Refer to Note 1 f) for additional information. At December 31, 2010 and 2009, 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. Refer to Note 1 f) for additional information. At December 31, 2010, the cash balance of one or more entities was negative; however, the overall Pool balances were positive.

[3] ACE maintains two notional multi-currency cash pools (Pools) with a third-party bank. Refer to Note 1f) for additional information. At December 31, 2012, the cash balance of one or more entities was negative; however, the overall Pool balances were positive.

[4] ACE maintains two notional multi-currency cash pools (Pools) with a third-party bank. Refer to Note 1 f) for additional information. At December 31, 2012, the cash balance of one or more entities was negative; however, the overall Pool balances were positive.

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

[6] Includes ACE Limited parent company eliminations

[7] Includes ACE Limited parent company eliminations.