Information Provided In Connection With Outstanding Debt Of Subsidiaries (Condensed Consolidating Balance Sheet) (Detail) - USD ($) $ in Millions		Sep. 30, 2020		Dec. 31, 2019		Sep. 30, 2019	Dec. 31, 2018
Condensed Balance Sheet Statements, Captions [Line Items]
Investments		$ 116,047		$ 109,234
Cash		1,707	[1]	1,537	[2]
Restricted cash		166		109
Insurance and reinsurance balances receivable		10,588		10,357
Reinsurance recoverable on losses and loss expenses		15,670		15,181
Reinsurance recoverable on policy benefits		203		197
Operating Lease, Right-of-Use Asset		470		551
Value of business acquired		286		306
Goodwill and other intangible assets		21,103		21,359
Investments in subsidiaries		0		0
Due from subsidiaries and affiliates, net		0		0
Other assets		22,016		18,663
Total assets		187,786		176,943
Unpaid losses and loss expenses		67,905		62,690		$ 63,012	$ 62,960
Unearned premiums		17,502		16,771
Future policy benefits		5,955		5,814
Due to subsidiaries and affiliates, net		0		0
Affiliated notional cash pooling programs		0
Operating Lease, Liability		517		603
Repurchase agreements		1,413		1,416
Short-term debt		1,300		1,299
Long-term debt		14,830		13,559
Trust preferred securities		308		308
Other liabilities		22,160		19,755
Total liabilities		131,373		121,612
Total shareholders' equity		56,413		55,331		$ 54,572
Total liabilities and shareholders’ equity		187,786		176,943
Chubb Limited (Parent Guarantor)
Condensed Balance Sheet Statements, Captions [Line Items]
Investments		0		0
Cash		31	[1]	2	[2]
Restricted cash		0		0
Insurance and reinsurance balances receivable		0		0
Reinsurance recoverable on 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		53,715		50,853
Due from subsidiaries and affiliates, net		2,991		4,776
Other assets		8		12
Total assets		56,745		55,643
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	[1]	0
Repurchase agreements		0		0
Short-term debt		0		0
Long-term debt		0		0
Trust preferred securities		0		0
Other liabilities		332		312
Total liabilities		332		312
Total shareholders' equity		56,413		55,331
Total liabilities and shareholders’ equity		56,745		55,643
Chubb INA Holdings Inc (Subsidiary Issuer)
Condensed Balance Sheet Statements, Captions [Line Items]
Investments		724		1,013
Cash		0	[1]	442	[2]
Restricted cash		0		0
Insurance and reinsurance balances receivable		0		0
Reinsurance recoverable on 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		54,125		52,076
Due from subsidiaries and affiliates, net		0		0
Other assets		391		408
Total assets		55,240		53,939
Unpaid losses and loss expenses		0		0
Unearned premiums		0		0
Future policy benefits		0		0
Due to subsidiaries and affiliates, net		3,162		4,446
Affiliated notional cash pooling programs	[1]	123
Repurchase agreements		0		0
Short-term debt		1,300		1,298
Long-term debt		14,830		13,559
Trust preferred securities		308		308
Other liabilities		1,374		1,649
Total liabilities		21,097		21,260
Total shareholders' equity		34,143		32,679
Total liabilities and shareholders’ equity		55,240		53,939
Other Chubb Limited Subsidiaries
Condensed Balance Sheet Statements, Captions [Line Items]
Investments		115,323		108,221
Cash		1,799	[1]	1,093	[2]
Restricted cash		166		109
Insurance and reinsurance balances receivable		13,684		12,920
Reinsurance recoverable on losses and loss expenses		25,482		24,780
Reinsurance recoverable on policy benefits		298		292
Value of business acquired		286		306
Goodwill and other intangible assets		21,103		21,359
Investments in subsidiaries		0		0
Due from subsidiaries and affiliates, net		171		0
Other assets		23,459		20,072
Total assets		201,771		189,152
Unpaid losses and loss expenses		77,467		71,916
Unearned premiums		18,695		17,978
Future policy benefits		6,050		5,909
Due to subsidiaries and affiliates, net		0		330
Affiliated notional cash pooling programs	[1]	0
Repurchase agreements		1,413		1,416
Short-term debt		0		1
Long-term debt		0		0
Trust preferred securities		0		0
Other liabilities		24,449		21,352
Total liabilities		128,074		118,902
Total shareholders' equity		73,697		70,250
Total liabilities and shareholders’ equity		201,771		189,152
Consolidating Adjustments and Eliminations
Condensed Balance Sheet Statements, Captions [Line Items]
Investments		0		0
Cash		(123)	[1]	0	[2]
Restricted cash		0		0
Insurance and reinsurance balances receivable		(3,096)		(2,563)
Reinsurance recoverable on losses and loss expenses		(9,812)		(9,599)
Reinsurance recoverable on policy benefits		(95)		(95)
Value of business acquired		0		0
Goodwill and other intangible assets		0		0
Investments in subsidiaries		(107,840)		(102,929)
Due from subsidiaries and affiliates, net		(3,162)		(4,776)
Other assets		(1,842)		(1,829)
Total assets		(125,970)		(121,791)
Unpaid losses and loss expenses		(9,562)		(9,226)
Unearned premiums		(1,193)		(1,207)
Future policy benefits		(95)		(95)
Due to subsidiaries and affiliates, net		(3,162)		(4,776)
Affiliated notional cash pooling programs	[1]	(123)
Repurchase agreements		0		0
Short-term debt		0		0
Long-term debt		0		0
Trust preferred securities		0		0
Other liabilities		(3,995)		(3,558)
Total liabilities		(18,130)		(18,862)
Total shareholders' equity		(107,840)		(102,929)
Total liabilities and shareholders’ equity		$ (125,970)		$ (121,791)

[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, 2020, 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 the 2019 Form 10-K for additional information.