Information Provided In Connection With Outstanding Debt Of Subsidiaries (Condensed Consolidating Statement Of Operations) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Information Provided In Connection With Outstanding Debt Of Subsidiaries [Line Items]
Net premiums written	$ 4,076	$ 4,185
Net premiums earned	3,927	3,970
Net investment income	551	553
Equity in earnings of subsidiaries	0	0
Net realized gains (losses) including OTTI	(89)	(104)
Losses and loss expenses	2,122	2,161
Policy benefits	142	114
Policy acquisition costs and administrative expenses	1,261	1,263
Interest (income) expense	68	71
Other (income) expense	(5)	(17)
Income tax expense (benefit)	120	93
Net income (loss)	681	734
Comprehensive income (loss)	642	1,108
ACE Limited (Parent Guarantor)
Information Provided In Connection With Outstanding Debt Of Subsidiaries [Line Items]
Net premiums written	0	0
Net premiums earned	0	0
Net investment income	1	0
Equity in earnings of subsidiaries	648	702
Net realized gains (losses) including OTTI	0	0
Losses and loss expenses	0	0
Policy benefits	0	0
Policy acquisition costs and administrative expenses	14	17
Interest (income) expense	(8)	(10)
Other (income) expense	(41)	(42)
Income tax expense (benefit)	3	3
Net income (loss)	681	734
Comprehensive income (loss)	642	1,108
ACE INA Holdings Inc (Subsidiary Issuer)
Information Provided In Connection With Outstanding Debt Of Subsidiaries [Line Items]
Net premiums written	0	0
Net premiums earned	0	0
Net investment income	1	0
Equity in earnings of subsidiaries	204	180
Net realized gains (losses) including OTTI	0	(1)
Losses and loss expenses	0	0
Policy benefits	0	0
Policy acquisition costs and administrative expenses	6	6
Interest (income) expense	69	71
Other (income) expense	(3)	14
Income tax expense (benefit)	(26)	(30)
Net income (loss)	159	118
Comprehensive income (loss)	24	266
Other ACE Limited Subsidiaries
Information Provided In Connection With Outstanding Debt Of Subsidiaries [Line Items]
Net premiums written	4,076	4,185
Net premiums earned	3,927	3,970
Net investment income	549	553
Equity in earnings of subsidiaries	0	0
Net realized gains (losses) including OTTI	(89)	(103)
Losses and loss expenses	2,122	2,161
Policy benefits	142	114
Policy acquisition costs and administrative expenses	1,241	1,240
Interest (income) expense	7	10
Other (income) expense	39	11
Income tax expense (benefit)	143	120
Net income (loss)	693	764
Comprehensive income (loss)	654	1,138
Consolidating Adjustments and Eliminations
Information Provided In Connection With Outstanding Debt Of Subsidiaries [Line Items]
Net premiums written	0	0
Net premiums earned	0	0
Net investment income	0	0
Equity in earnings of subsidiaries	(852)	(882)
Net realized gains (losses) including OTTI	0	0
Losses and loss expenses	0	0
Policy benefits	0	0
Policy acquisition costs and administrative expenses	0	0
Interest (income) expense	0	0
Other (income) expense	0	0
Income tax expense (benefit)	0	0
Net income (loss)	(852)	(882)
Comprehensive income (loss)	$ (678)	$ (1,404)