Information Provided In Connection With Outstanding Debt Of Subsidiaries (Condensed Consolidating Balance Sheet) (Detail) - USD ($) $ in Millions		Sep. 30, 2018		Dec. 31, 2017		Sep. 30, 2017	Dec. 31, 2016
Condensed Balance Sheet Statements, Captions [Line Items]
Investments		$ 101,163		$ 102,444
Cash		1,053	[1]	728	[2]
Restricted Cash	[1]	104		123
Insurance and reinsurance balances receivable		10,193		9,334
Reinsurance Recoverable Losses And Loss Expenses		15,088		15,034
Reinsurance recoverable on policy benefits		206		184
Value of business acquired		298		326
Goodwill and other intangible assets		21,471		22,054
Investments in subsidiaries		0		0
Due from subsidiaries and affiliates, net		0		0
Other assets		18,108		16,795
Total assets		167,684		167,022
Unpaid losses and loss expenses		63,029		63,179		$ 64,153	$ 60,540
Unearned premiums		15,725		15,216
Future policy benefits		5,463		5,321
Due to subsidiaries and affiliates, net		0		0
Affiliated notional cash pooling programs		0		0
Repurchase agreements		1,414		1,408
Short-term debt		500		1,013
Long-term debt		12,149		11,556
Trust preferred securities		308		308
Other liabilities		18,162		17,849
Total liabilities		116,750		115,850
Total shareholders' equity		50,934		51,172		$ 50,471
Total liabilities and shareholders’ equity		167,684		167,022
Chubb Limited (Parent Guarantor)
Condensed Balance Sheet Statements, Captions [Line Items]
Investments		0		0
Cash		0	[1]	3	[2]
Restricted Cash	[1]	0		0
Insurance and reinsurance balances receivable		0		0
Reinsurance Recoverable Losses And Loss Expenses		0		0
Reinsurance recoverable on policy benefits		0		0
Value of business acquired		0		0
Goodwill and other intangible assets		0		0
Investments in subsidiaries		43,528		41,909
Due from subsidiaries and affiliates, net		7,917		9,639
Other assets		3		3
Total assets		51,448		51,554
Unpaid losses and loss expenses		0		0
Unearned premiums		0		0
Future policy benefits		0		0
Due to subsidiaries and affiliates, net		0		0
Affiliated notional cash pooling programs		165	[1]	0	[2]
Repurchase agreements		0		0
Short-term debt		0		0
Long-term debt		0		0
Trust preferred securities		0		0
Other liabilities		349		382
Total liabilities		514		382
Total shareholders' equity		50,934		51,172
Total liabilities and shareholders’ equity		51,448		51,554
Chubb INA Holdings Inc (Subsidiary Issuer)
Condensed Balance Sheet Statements, Captions [Line Items]
Investments		183		168
Cash		1	[1]	1	[2]
Restricted Cash	[1]	0		0
Insurance and reinsurance balances receivable		0		0
Reinsurance Recoverable Losses And Loss Expenses		0		0
Reinsurance recoverable on policy benefits		0		0
Value of business acquired		0		0
Goodwill and other intangible assets		0		0
Investments in subsidiaries		50,132		51,165
Due from subsidiaries and affiliates, net		0		0
Other assets		678		287
Total assets		50,994		51,621
Unpaid losses and loss expenses		0		0
Unearned premiums		0		0
Future policy benefits		0		0
Due to subsidiaries and affiliates, net		8,028		9,432
Affiliated notional cash pooling programs		81	[1]	115	[2]
Repurchase agreements		0		0
Short-term debt		500		1,013
Long-term debt		12,138		11,546
Trust preferred securities		308		308
Other liabilities		2,418		1,411
Total liabilities		23,473		23,825
Total shareholders' equity		27,521		27,796
Total liabilities and shareholders’ equity		50,994		51,621
Other Chubb Limited Subsidiaries
Condensed Balance Sheet Statements, Captions [Line Items]
Investments		100,980		102,276
Cash		1,298	[1]	839	[2]
Restricted Cash	[1]	104		123
Insurance and reinsurance balances receivable		10,486		10,820
Reinsurance Recoverable Losses And Loss Expenses		26,408		27,514
Reinsurance recoverable on policy benefits		1,109		1,194
Value of business acquired		298		326
Goodwill and other intangible assets		21,471		22,054
Investments in subsidiaries		0		0
Due from subsidiaries and affiliates, net		111		0
Other assets		18,985		20,578
Total assets		181,250		185,724
Unpaid losses and loss expenses		73,422		74,767
Unearned premiums		16,793		18,875
Future policy benefits		6,366		6,331
Due to subsidiaries and affiliates, net		0		207
Affiliated notional cash pooling programs		0	[1]	0	[2]
Repurchase agreements		1,414		1,408
Short-term debt		0		0
Long-term debt		11		10
Trust preferred securities		0		0
Other liabilities		17,105		18,848
Total liabilities		115,111		120,446
Total shareholders' equity		66,139		65,278
Total liabilities and shareholders’ equity		181,250		185,724
Consolidating Adjustments and Eliminations
Condensed Balance Sheet Statements, Captions [Line Items]
Investments		0		0
Cash		(246)	[1]	(115)	[2]
Restricted Cash	[1]	0		0
Insurance and reinsurance balances receivable		(293)		(1,486)
Reinsurance Recoverable Losses And Loss Expenses		(11,320)		(12,480)
Reinsurance recoverable on policy benefits		(903)		(1,010)
Value of business acquired		0		0
Goodwill and other intangible assets		0		0
Investments in subsidiaries		(93,660)		(93,074)
Due from subsidiaries and affiliates, net		(8,028)		(9,639)
Other assets		(1,558)		(4,073)
Total assets		(116,008)		(121,877)
Unpaid losses and loss expenses		(10,393)		(11,588)
Unearned premiums		(1,068)		(3,659)
Future policy benefits		(903)		(1,010)
Due to subsidiaries and affiliates, net		(8,028)		(9,639)
Affiliated notional cash pooling programs		(246)	[1]	(115)	[2]
Repurchase agreements		0		0
Short-term debt		0		0
Long-term debt		0		0
Trust preferred securities		0		0
Other liabilities		(1,710)		(2,792)
Total liabilities		(22,348)		(28,803)
Total shareholders' equity		(93,660)		(93,074)
Total liabilities and shareholders’ equity		$ (116,008)		$ (121,877)

[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, 2018, 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 December 31, 2017, the cash balance of one or more entities was negative; however, the overall Pool balances were positive.