Information Provided In Connection With Outstanding Debt Of Subsidiaries (Condensed Consolidating Statement Of Operations) (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Information Provided In Connection With Outstanding Debt Of Subsidiaries [Line Items]
Net premiums written	$ 4,709	$ 4,729	$ 13,569	$ 13,473
Net premiums earned	4,719	4,754	13,006	13,056
Net investment income	549	566	1,662	1,675
Equity in earnings of subsidiaries	0	0	0	0
Net realized gains (losses) including OTTI	(397)	(120)	(360)	(297)
Losses and loss expenses	2,643	2,684	7,182	7,233
Policy benefits	89	125	384	383
Policy acquisition costs and administrative expenses	1,339	1,379	3,905	3,966
Interest (income) expense	68	70	207	213
Other (income) expense	12	(46)	(61)	(139)
Amortization of intangible assets	51	27	136	78
Chubb integration expenses	9	0	9	0
Income tax expense (benefit)	132	176	395	402
Net income (loss)	528	785	2,151	2,298
Comprehensive income (loss)	(271)	298	768	2,754
ACE Limited (Parent Guarantor)
Information Provided In Connection With Outstanding Debt Of Subsidiaries [Line Items]
Net premiums written	0	0	0	0
Net premiums earned	0	0	0	0
Net investment income	1	1	2	2
Equity in earnings of subsidiaries	488	745	2,037	2,192
Net realized gains (losses) including OTTI	0	0	0	0
Losses and loss expenses	0	0	0	0
Policy benefits	0	0	0	0
Policy acquisition costs and administrative expenses	15	18	47	57
Interest (income) expense	(8)	(7)	(23)	(26)
Other (income) expense	(51)	(54)	(149)	(146)
Amortization of intangible assets	0	0	0	0
Chubb integration expenses	1		1
Income tax expense (benefit)	4	4	12	11
Net income (loss)	528	785	2,151	2,298
Comprehensive income (loss)	(271)	298	768	2,754
ACE INA Holdings Inc (Subsidiary Issuer)
Information Provided In Connection With Outstanding Debt Of Subsidiaries [Line Items]
Net premiums written	0	0	0	0
Net premiums earned	0	0	0	0
Net investment income	1	0	2	1
Equity in earnings of subsidiaries	255	258	755	669
Net realized gains (losses) including OTTI	(4)	46	(6)	53
Losses and loss expenses	0	0	0	0
Policy benefits	0	0	0	0
Policy acquisition costs and administrative expenses	7	6	20	20
Interest (income) expense	68	68	206	209
Other (income) expense	(5)	2	(12)	22
Amortization of intangible assets	0	0	0	0
Chubb integration expenses	8		8
Income tax expense (benefit)	(31)	(11)	(84)	(66)
Net income (loss)	205	239	613	538
Comprehensive income (loss)	(265)	33	(332)	810
Other ACE Limited Subsidiaries
Information Provided In Connection With Outstanding Debt Of Subsidiaries [Line Items]
Net premiums written	4,709	4,729	13,569	13,473
Net premiums earned	4,719	4,754	13,006	13,056
Net investment income	547	565	1,658	1,672
Equity in earnings of subsidiaries	0	0	0	0
Net realized gains (losses) including OTTI	(393)	(166)	(354)	(350)
Losses and loss expenses	2,643	2,684	7,182	7,233
Policy benefits	89	125	384	383
Policy acquisition costs and administrative expenses	1,317	1,355	3,838	3,889
Interest (income) expense	8	9	24	30
Other (income) expense	68	6	100	(15)
Amortization of intangible assets	51	27	136	78
Chubb integration expenses	0		0
Income tax expense (benefit)	159	183	467	457
Net income (loss)	538	764	2,179	2,323
Comprehensive income (loss)	(262)	276	795	2,778
Consolidating Adjustments and Eliminations
Information Provided In Connection With Outstanding Debt Of Subsidiaries [Line Items]
Net premiums written	0	0	0	0
Net premiums earned	0	0	0	0
Net investment income	0	0	0	0
Equity in earnings of subsidiaries	(743)	(1,003)	(2,792)	(2,861)
Net realized gains (losses) including OTTI	0	0	0	0
Losses and loss expenses	0	0	0	0
Policy benefits	0	0	0	0
Policy acquisition costs and administrative expenses	0	0	0	0
Interest (income) expense	0	0	0	0
Other (income) expense	0	0	0	0
Amortization of intangible assets	0	0	0	0
Chubb integration expenses	0		0
Income tax expense (benefit)	0	0	0	0
Net income (loss)	(743)	(1,003)	(2,792)	(2,861)
Comprehensive income (loss)	$ 527	$ (309)	$ (463)	$ (3,588)