Information Provided In Connection With Outstanding Debt Of Subsidiaries (Condensed Consolidating Statement Of Cash Flows) (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 cash flows from operating activities	$ 913		$ 572
Purchases of fixed maturities available for sale	(6,152)		(5,483)
Purchases of fixed maturities held to maturity	(142)		(32)
Purchases of equity securities	(107)		(19)
Sales of fixed maturities available for sale	2,764		3,795
Sales of equity securities	31		26
Maturities and redemptions of fixed maturities available for sale	2,016		1,076
Maturities and redemptions of fixed maturities held to maturity	491		345
Net derivative instruments settlements	(279)		(195)
Acquisition of subsidiaries	(33)		(25)
Other	(55)		(103)
Net cash flows used for investing activities	(1,466)		(615)
Dividends paid on Common Shares	(2)		(159)
Common Shares repurchased	(154)		(11)
Proceeds from issuance of long-term debt	947		0
Net proceeds from (repayments) issuance of short-term debt	1		281
Proceeds from share-based compensation plans, including windfall tax benefits	21		28
Net cash flows from financing activities	813		139
Effect of foreign currency rate changes on cash and cash equivalents	(20)		5
Net increase (decrease) in cash	240		101
Cash - beginning of period	615	[1]	614
Cash - end of period	855		715
Parent Company [Member]
Information Provided In Connection With Outstanding Debt Of Subsidiaries [Line Items]
Net cash flows from operating activities	53		19
Sales of fixed maturities available for sale			0
Net derivative instruments settlements	0		(1)
Advances from (to) affiliates	43		66
Net cash flows used for investing activities	43		65
Dividends paid on Common Shares	(2)		(159)
Net proceeds from (repayments) issuance of short-term debt			130
Proceeds from share-based compensation plans, including windfall tax benefits	0		1
Net cash flows from financing activities	(2)		(28)
Net increase (decrease) in cash	94		56
Cash - beginning of period	103	[1]	106
Cash - end of period	197		162
Guarantor Subsidiaries [Member]
Information Provided In Connection With Outstanding Debt Of Subsidiaries [Line Items]
Net cash flows from operating activities	644		66
Purchases of fixed maturities available for sale	(3,825)		(2,650)
Purchases of fixed maturities held to maturity	(137)		(31)
Purchases of equity securities	(89)		(10)
Sales of fixed maturities available for sale	1,473		1,935
Sales of equity securities	25		24
Maturities and redemptions of fixed maturities available for sale	879		497
Maturities and redemptions of fixed maturities held to maturity	351		267
Net derivative instruments settlements	4		(1)
Acquisition of subsidiaries	(33)		(25)
Other	(86)		90
Net cash flows used for investing activities	(1,438)		96
Proceeds from issuance of long-term debt	947
Net proceeds from (repayments) issuance of short-term debt	0		1
Proceeds from share-based compensation plans, including windfall tax benefits	(8)	[2]
Advances (to) from affiliates	(71)		(48)
Net cash flows from financing activities	868		(47)
Effect of foreign currency rate changes on cash and cash equivalents	(29)		(1)
Net increase (decrease) in cash	45		114
Cash - beginning of period	515	[1]	382
Cash - end of period	560		496
Other ACE Limited Subsidiaries And Eliminations [Member]
Information Provided In Connection With Outstanding Debt Of Subsidiaries [Line Items]
Net cash flows from operating activities	216	[2]	487	[2]
Purchases of fixed maturities available for sale	(2,327)	[2]	(2,833)	[2]
Purchases of fixed maturities held to maturity	(5)	[2]	(1)	[2]
Purchases of equity securities	(18)	[2]	(9)	[2]
Sales of fixed maturities available for sale	1,291	[2]	1,860	[2]
Sales of equity securities	6	[2]	2	[2]
Maturities and redemptions of fixed maturities available for sale	1,137	[2]	579	[2]
Maturities and redemptions of fixed maturities held to maturity	140	[2]	78	[2]
Net derivative instruments settlements	(283)	[2]	(193)	[2]
Acquisition of subsidiaries	0	[2]	0	[2]
Other	31	[2]	(193)	[2]
Net cash flows used for investing activities	(28)	[2]	(710)	[2]
Dividends paid on Common Shares	0	[2]
Common Shares repurchased	(154)	[2]	(11)	[2]
Net proceeds from (repayments) issuance of short-term debt	1	[2]	150	[2]
Proceeds from share-based compensation plans, including windfall tax benefits	29	[2]	27	[2]
Advances (to) from affiliates	28	[2]	(18)	[2]
Net cash flows from financing activities	(96)	[2]	148	[2]
Effect of foreign currency rate changes on cash and cash equivalents	9	[2]	6	[2]
Net increase (decrease) in cash	101	[2]	(69)	[2]
Cash - beginning of period	(3)	[1],[2]	126	[2]
Cash - end of period	98	[2]	57	[2]
Consolidation, Eliminations [Member]
Information Provided In Connection With Outstanding Debt Of Subsidiaries [Line Items]
Net cash flows from operating activities			0	[3]
Advances from (to) affiliates	(43)	[3]	(66)	[3]
Net cash flows used for investing activities	(43)	[3]	(66)	[3]
Advances (to) from affiliates	43	[3]	66	[3]
Net cash flows from financing activities	$ 43	[3]	$ 66	[3]

[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 December 31, 2012, the cash balance of one or more entities was negative; however, the overall Pool balances were positive.

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

[3] Includes ACE Limited parent company eliminations.