Acquisitions (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	Jun. 17, 2014	Sep. 30, 2015		Jun. 30, 2015	Apr. 01, 2015	Dec. 31, 2014		Oct. 31, 2014	Sep. 30, 2014	[4]	Apr. 28, 2014	Dec. 31, 2013	[4]
Business Acquisition [Line Items]
Unpaid losses and loss expenses		$ 37,564				$ 38,315
Unearned premiums		8,510				8,222
Insurance and reinsurance balances receivable		5,290				5,426
Cash		$ 1,038	[1],[2]			$ 655	[1],[3]		$ 806			$ 579
ACE share price		$ 103.40		$ 101.68
Fireman's Fund high net worth personal lines [Member]
Business Acquisition [Line Items]
Goodwill					$ 196
Other intangible assets					278
Purchase price					365
Assumed liabilities fair value					858
Unpaid losses and loss expenses					402
Unearned premiums					428
Insurance and reinsurance balances receivable					128
Cash					620
Acquired assets fair value					$ 749
Large Corporate Property And Casualty Business Of Itau Seguros [Member]
Business Acquisition [Line Items]
Goodwill								$ 445
Other intangible assets								60
Purchase price								$ 606
The Siam Commercial Samaggi Insurance PCL [Member]
Business Acquisition [Line Items]
Percentage ownership acquired	32.17%										60.86%
Goodwill											$ 46
Other intangible assets											$ 80
Total Ownership Percentage	93.03%
Purchase price for total ownership percentage	$ 176
The Chubb Corporation [Member]
Business Acquisition [Line Items]
Cash purchase price per share		62.93
Number of ACE shares to be issued per share		$ 0.6019
Expected purchase price		$ 28,800		$ 28,300
Approximate number of shares to be issued		137
Approximate ownership percentage of new company		30.00%
Expected cash to be used to finance acquisition		$ 9,000
Senior notes issued to finance acquisition		$ 5,300

[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, 2015 and December 31, 2014, the cash balance of one or more entities was negative; however, the overall Pool balances were positive.

[2] 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, 2015, the cash balance of one or more entities was negative; however, the overall Pool balances were positive.

[3] 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, 2014, the cash balance of one or more entities was negative; however, the overall Pool balances were positive.

[4] 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, 2014 and December 31, 2013, the cash balance of one or more entities was negative; however, the overall Pool balances were positive.