Acquisitions (Detail) $ / shares in Units, $ in Millions			3 Months Ended				9 Months Ended
	Jan. 14, 2016 USD ($) $ / shares shares	Apr. 01, 2015 USD ($)	Sep. 30, 2016 USD ($) shares		Sep. 30, 2015 USD ($) shares		Sep. 30, 2016 USD ($) shares		Sep. 30, 2015 USD ($) shares		Dec. 31, 2015 USD ($)		Dec. 31, 2014 USD ($)	[3]
Business Acquisition [Line Items]
Other intangible assets			$ 6,991				$ 6,991				$ 887
Weighted-average shares outstanding | shares			468,021,093		324,210,936		460,631,794		325,904,502
Cash			$ 870	[1],[2]	$ 1,038	[3]	$ 870	[1],[2]	$ 1,038	[3]	1,775	[1],[4]	$ 655
Investments			101,036				101,036				66,251
Accrued investment income			915				915				513
Insurance and reinsurance balances receivable			8,493				8,493				5,323
Reinsurance recoverable on losses and loss expenses			13,448				13,448				11,386
Prepaid reinsurance premiums			2,449				2,449				2,082
Other assets			5,521				5,521				3,821
Unpaid losses and loss expenses			(61,347)				(61,347)				(37,303)
Unearned premiums			(15,054)				(15,054)				(8,439)
Insurance and reinsurance balances payable			(4,885)				(4,885)				(4,270)
Accounts payable, accrued expenses, and other liabilities			(9,748)				(9,748)				(6,205)
Long-term debt			(12,621)				(12,621)				(9,389)
Goodwill			15,481				15,481				$ 4,796
Chubb integration expenses			$ 115		9		361		9
The Chubb Corporation [Member]
Business Acquisition [Line Items]
Purchase price	$ 29,500
Goodwill, Purchase Accounting Adjustment							$ 85
Business Acquisition, Financing Of Acquisition With Cash	9,000
Senior notes issued to finance acquisition	$ 5,300
Weighted-average shares outstanding | shares	228,000,000
Per share exchange ratio	0.6019
Common shares issued by Chubb Limited | shares	137,000,000
Share Price | $ / shares	$ 111.02
Fair value of common shares issued by Chubb Limited to common shareholders of Chubb Corp	$ 15,204
Agreed cash price per share paid to common shareholders of Chubb Corp | $ / shares	$ 62.93
Payments to Acquire Businesses, Gross	$ 14,319
Attributed Value Equity Awards Assumed in Acquisition	323
Purchase price	29,846
Cash	71
Investments	42,967
Accrued investment income	337
Insurance and reinsurance balances receivable	2,981
Reinsurance recoverable on losses and loss expenses	1,645
Indefinite-Lived Intangible Assets	2,860
Finite lived intangible assets	4,795
Prepaid reinsurance premiums	280
Other assets	865
Unpaid losses and loss expenses	(22,906)
Unearned premiums	(7,033)
Insurance and reinsurance balances payable	(511)
Accounts payable, accrued expenses, and other liabilities	(1,935)
Deferred Tax Liabilities, Net	(1,335)
Long-term debt	(3,765)
Total identifiable net assets acquired	19,316
Goodwill	10,530
Chubb integration expenses					$ 9
Total Value of Equity Awards Issued in Acquisition	525
Fireman's Fund high net worth personal lines [Member]
Business Acquisition [Line Items]
Acquired assets fair value		$ 753
Other intangible assets		278
Payments to Acquire Businesses, Gross		365
Cash		629
Insurance and reinsurance balances receivable		124
Unpaid losses and loss expenses		(417)
Unearned premiums		(428)
Goodwill		196
Assumed liabilities fair value		$ 863
Minimum [Member]
Business Acquisition [Line Items]
Estimated Useful Life							1 year
Maximum [Member]
Business Acquisition [Line Items]
Estimated Useful Life							24 years
Additional Paid-in Capital [Member]
Business Acquisition [Line Items]
Attributed Value Equity Awards Assumed in Acquisition							$ (365)		(157)
Additional Paid-in Capital [Member] | The Chubb Corporation [Member]
Business Acquisition [Line Items]
Attributed Value Equity Awards Assumed in Acquisition	$ 323						$ 323		$ 0

[1] Chubb maintains two notional multicurrency cash pools (Pools) with a third-party bank. Various Chubb entities participate in one or the other of the Pools, pursuant to which credit and debit balances in individual Chubb accounts are translated daily into a single currency and pooled on a notional basis. Individual Chubb entities are permitted to overdraw on their individual accounts provided the overall Pool balances do not fall below zero. At September 30, 2016 and December 31, 2015, the cash balance of one or more entities was negative; however, the overall Pool balances were positive.

[2] Chubb maintains two notional multicurrency cash pools (Pools) with a third-party bank. Various Chubb entities participate in one or the other of the Pools, pursuant to which credit and debit balances in individual Chubb accounts are translated daily into a single currency and pooled on a notional basis. Individual Chubb entities are permitted to overdraw on their individual accounts provided the overall Pool balances do not fall below zero. At September 30, 2016, the cash balance of one or more entities was negative; however, the overall Pool balances were positive.

[3] Chubb maintains two notional multicurrency cash pools (Pools) with a third-party bank. Various Chubb entities participate in one or the other of the Pools, pursuant to which credit and debit balances in individual Chubb accounts are translated daily into a single currency and pooled on a notional basis. Individual Chubb 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.

[4] Chubb maintains two notional multicurrency cash pools (Pools) with a third-party bank. Various Chubb entities participate in one or the other of the Pools, pursuant to which credit and debit balances in individual Chubb accounts are translated daily into a single currency and pooled on a notional basis. Individual Chubb entities are permitted to overdraw on their individual accounts provided the overall Pool balances do not fall below zero. At December 31, 2015, the cash balance of one or more entities was negative; however, the overall Pool balances were positive.