Acquisitions (Detail) $ / shares in Units, $ in Millions			12 Months Ended
		Jan. 14, 2016 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) shares		Dec. 31, 2016 USD ($) $ / shares shares		Dec. 31, 2016 USD ($)		Dec. 31, 2015 USD ($) $ / shares shares		Apr. 01, 2015 USD ($)	Dec. 31, 2014 USD ($)
Business Acquisition [Line Items]
Weighted Average Number of Shares Outstanding, Basic | shares			467,145,716		462,519,789				325,589,361
Cash			$ 728	[1],[2]	$ 985	[1],[3],[4]	$ 985	[1],[3],[4]	$ 1,775	[1],[5]		$ 655	[5]
Investments			102,444		99,094		99,094
Accrued investment income			909		918		918
Insurance and reinsurance balances receivable			9,334		8,970		8,970
Reinsurance recoverable on paid losses and loss expenses	[6]		15,034		13,577		13,577
Prepaid reinsurance premiums			2,529		2,448		2,448
Other assets			6,358		5,090		5,090
Unpaid losses and loss expenses			(63,179)		(60,540)		(60,540)		(37,303)			$ (38,315)
Unearned premiums			(15,216)		(14,779)		(14,779)
Reinsurance Payable			(5,868)		(5,637)		(5,637)
Accounts Payable, Accrued Expenses and Other Liabilities			(9,545)		(8,617)		(8,617)
Deferred Tax Liabilities, Net			(699)		(988)		(988)
Long-term Debt			(11,556)		(12,610)		(12,610)
Intangible Assets, Net (Excluding Goodwill)			6,513		6,763		6,763
Goodwill			15,541		15,332		15,332		4,796
Common Shares (CHF 24.15 par value; 479,783,864 shares issued; 463,833,179 and 465,968,716 shares outstanding)			$ 11,121		11,121		11,121
Fireman's Fund high net worth personal lines [Member]
Business Acquisition [Line Items]
Business Acquisition, Financing Of Acquisition With Cash											$ 365
Cash											629
Insurance and reinsurance balances receivable											124
Unpaid losses and loss expenses											(417)
Unearned premiums											(428)
Fair Value of Assets Acquired											753
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities											863
Intangible Assets, Net (Excluding Goodwill)											278
Goodwill											$ 196
The Chubb Corporation [Member]
Business Acquisition [Line Items]
Total Value of Equity Awards Issued in Acquisition		$ 525
Purchase Price		29,500
Business Acquisition, Financing Of Acquisition With Cash		9,000
Senior notes issued to finance acquisition		$ 5,300
Weighted Average Number of Shares Outstanding, Basic | shares		228,000,000
Shares Conversion Ratio in Acquisition		0.6019
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares | shares		137,000,000
Share Price | $ / shares		$ 111.02
Equity Issued in Business Combination, Fair Value Disclosure		$ 15,204
Business Acquisition, Share Price | $ / shares		$ 62.93
Payments to Acquire Businesses, Gross		$ 14,319
Attributed Value Equity Awards Assumed in Acquisition	[7]	323
Business Combination, Consideration Transferred		29,846
Cash		71
Investments		42,967
Accrued investment income		359
Insurance and reinsurance balances receivable		3,095
Reinsurance recoverable on paid losses and loss expenses		1,676
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets		2,860
Finite lived intangible assets		4,795
Prepaid reinsurance premiums		280
Other assets		853
Unpaid losses and loss expenses		(22,923)
Unearned premiums		(7,011)
Reinsurance Payable		(603)
Accounts Payable, Accrued Expenses and Other Liabilities		(2,030)
Deferred Tax Liabilities, Net		(1,292)
Long-term Debt		(3,765)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net		19,332
Goodwill		10,514
Goodwill, Expected Tax Deductible Amount		$ 0
Chubb Corp, Revenue since acquisition date							12,376
Chubb Corp, Earnings since acquisition date							$ 1,756
Chubb Corp, Pro Forma Revenue					31,937				32,622
Chubb Corp, Pro Forma Net Income (Loss)					$ 4,183				$ 4,478
Chubb Corp, Pro Forma Earnings Per Share, Basic | $ / shares					$ 8.95				$ 9.61
Chubb Corp, Pro Forma Earnings Per Share, Diluted | $ / shares					$ 8.88				$ 9.52

[1] Chubb maintains two notional multi-currency cash pools (Pools) with a third-party bank. Refer to Note 1 f) for additional information. At December 31, 2017 and 2016, 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. Refer to Note 1 f) for additional information. At December 31, 2017, the cash balance of one or more entities was negative; however, the overall Pool balances were positive.

[3] Chubb maintains two notional multi-currency cash pools (Pools) with a third-party bank. Refer to Note 1 f) for additional information. At December 31, 2016 and 2015, 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. Refer to Note 1 f) for additional information. At December 31, 2016, the cash balance of one or more entities was negative; however, the overall Pool balances were positive.

[5] Chubb maintains two notional multi-currency cash pools (Pools) with a third-party bank. Refer to Note 1 f) for additional information. At December 31, 2015 and 2014, the cash balance of one or more entities was negative; however, the overall Pool balances were positive.

[6] (1) Net of a provision for uncollectible reinsurance.

[7] (1) The fair value of the replacement equity awards was $525 million, of which $323 million was attributed to service periods prior to the acquisition and was included in the purchase consideration. Refer to Note 12 for further information on these replacement equity awards.