Information Provided In Connection With Outstanding Debt Of Subsidiaries (Condensed Consolidating Statement Of Cash Flows) (Detail) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020		Sep. 30, 2019
Condensed Cash Flow Statements, Captions [Line Items]
Net Cash Provided by (Used in) Operating Activities	$ 7,241		$ 4,913
Purchases of fixed maturities available for sale	(20,793)		(19,778)
Purchases of fixed maturities held to maturity	(42)		(143)
Purchases of equity securities	(3,622)		(466)
Proceeds From Sale Of Available For Sale Securities Debt Condensed	9,537		10,436
Sales of equity securities	1,526		577
Maturities and redemptions of fixed maturities available for sale	8,709		6,390
Maturities and redemptions of fixed maturities held to maturity	841		814
Net change in short-term investments	(434)		202
Net derivative instruments settlements	(74)		(647)
Private equity contribution	(1,056)		(1,093)
Private equity distribution	588		973
Payments for Other Deposits	(503)
Payments to Acquire Other Investments			(329)
Portion one of payments to acquire 22.4% of Huatai Group	(1,054)
Capital contribution	0		0
Other	(352)		(497)
Net cash flows used for investing activities	(6,729)		(3,561)
Dividends paid on Common Shares	(1,035)		(1,014)
Common Shares repurchased	(333)		(1,203)
Proceeds from Issuance of Long-term Debt	988		1,286
Repayments of Long-term Debt	0		(501)
Proceeds from issuance of repurchase agreements	1,402		2,394
Repayments of repurchase agreements	(1,402)		(2,396)
Proceeds from share-based compensation plans	77		155
Dividend to Parent Company	0		0
Advances (to) from affiliates	0		0
Capital contribution	0		0
Net proceeds from (payments to) affiliated notional cash pooling program	0	[1]	0	[2]
Policyholder contract deposits	322		376
Policyholder contract withdrawals	(253)		(221)
Net cash flows used for financing activities	(234)		(1,124)
Effect of foreign currency rate changes on cash and restricted cash	(51)		21
Net Increase (Decrease) in cash and restricted cash	227		249
Cash and restricted cash - beginning of period	1,646	[1]	1,340	[2]
Cash and restricted cash - end of period	1,873	[1]	1,589	[2]
Chubb Limited (Parent Guarantor)
Condensed Cash Flow Statements, Captions [Line Items]
Net Cash Provided by (Used in) Operating Activities	980		421
Purchases of fixed maturities available for sale	0		0
Purchases of fixed maturities held to maturity	0		0
Purchases of equity securities	0		0
Proceeds From Sale Of Available For Sale Securities Debt Condensed	0		0
Sales of equity securities	0		0
Maturities and redemptions of fixed maturities available for sale	0		0
Maturities and redemptions of fixed maturities held to maturity	0		0
Net change in short-term investments	0		0
Net derivative instruments settlements	0		0
Private equity contribution	0		0
Private equity distribution	0		0
Payments for Other Deposits	0
Payments to Acquire Other Investments			0
Portion one of payments to acquire 22.4% of Huatai Group	0
Capital contribution	(1,200)		(1,000)
Other	(2)		0
Net cash flows used for investing activities	(1,202)		(1,000)
Dividends paid on Common Shares	(1,035)		(1,014)
Common Shares repurchased	(333)		0
Proceeds from Issuance of Long-term Debt	0		0
Repayments of Long-term Debt			0
Proceeds from issuance of repurchase agreements	0		0
Repayments of repurchase agreements	0		0
Proceeds from share-based compensation plans	0		0
Dividend to Parent Company	0		0
Advances (to) from affiliates	1,621		996
Capital contribution	0		0
Net proceeds from (payments to) affiliated notional cash pooling program	0	[1]	593	[2]
Policyholder contract deposits	0		0
Policyholder contract withdrawals	0		0
Net cash flows used for financing activities	253		575
Effect of foreign currency rate changes on cash and restricted cash	(2)		5
Net Increase (Decrease) in cash and restricted cash	29		1
Cash and restricted cash - beginning of period	2	[1]	1	[2]
Cash and restricted cash - end of period	31	[1]	2	[2]
Chubb INA Holdings Inc (Subsidiary Issuer)
Condensed Cash Flow Statements, Captions [Line Items]
Net Cash Provided by (Used in) Operating Activities	(363)		1,118
Purchases of fixed maturities available for sale	(38)		(16)
Purchases of fixed maturities held to maturity	0		0
Purchases of equity securities	0		0
Proceeds From Sale Of Available For Sale Securities Debt Condensed	9		1
Sales of equity securities	0		0
Maturities and redemptions of fixed maturities available for sale	35		18
Maturities and redemptions of fixed maturities held to maturity	0		0
Net change in short-term investments	256		(5)
Net derivative instruments settlements	66		(55)
Private equity contribution	0		0
Private equity distribution	0		0
Payments for Other Deposits	0
Payments to Acquire Other Investments			0
Portion one of payments to acquire 22.4% of Huatai Group	0
Capital contribution	0		(110)
Other	(3)		(10)
Net cash flows used for investing activities	325		(177)
Dividends paid on Common Shares	0		0
Common Shares repurchased	0		0
Proceeds from Issuance of Long-term Debt	988		1,286
Repayments of Long-term Debt			(500)
Proceeds from issuance of repurchase agreements	0		0
Repayments of repurchase agreements	0		0
Proceeds from share-based compensation plans	0		0
Dividend to Parent Company	0		0
Advances (to) from affiliates	(1,511)		(1,715)
Capital contribution	0		0
Net proceeds from (payments to) affiliated notional cash pooling program	123	[1]	(15)	[2]
Policyholder contract deposits	0		0
Policyholder contract withdrawals	0		0
Net cash flows used for financing activities	(400)		(944)
Effect of foreign currency rate changes on cash and restricted cash	(4)		1
Net Increase (Decrease) in cash and restricted cash	(442)		(2)
Cash and restricted cash - beginning of period	442	[1]	2	[2]
Cash and restricted cash - end of period	0	[1]	0	[2]
Other Chubb Limited Subsidiaries
Condensed Cash Flow Statements, Captions [Line Items]
Net Cash Provided by (Used in) Operating Activities	7,714		5,234
Purchases of fixed maturities available for sale	(20,755)		(19,762)
Purchases of fixed maturities held to maturity	(42)		(143)
Purchases of equity securities	(3,622)		(466)
Proceeds From Sale Of Available For Sale Securities Debt Condensed	9,528		10,435
Sales of equity securities	1,526		577
Maturities and redemptions of fixed maturities available for sale	8,674		6,372
Maturities and redemptions of fixed maturities held to maturity	841		814
Net change in short-term investments	(690)		207
Net derivative instruments settlements	(140)		(592)
Private equity contribution	(1,056)		(1,093)
Private equity distribution	588		973
Payments for Other Deposits	(503)
Payments to Acquire Other Investments			(329)
Portion one of payments to acquire 22.4% of Huatai Group	(1,054)
Capital contribution	0		0
Other	(347)		(487)
Net cash flows used for investing activities	(7,052)		(3,494)
Dividends paid on Common Shares	0		0
Common Shares repurchased	0		(1,203)
Proceeds from Issuance of Long-term Debt	0		0
Repayments of Long-term Debt			(1)
Proceeds from issuance of repurchase agreements	1,402		2,394
Repayments of repurchase agreements	(1,402)		(2,396)
Proceeds from share-based compensation plans	77		155
Dividend to Parent Company	(1,090)		(1,860)
Advances (to) from affiliates	(110)		719
Capital contribution	1,200		1,110
Net proceeds from (payments to) affiliated notional cash pooling program	0	[1]	0	[2]
Policyholder contract deposits	322		376
Policyholder contract withdrawals	(253)		(221)
Net cash flows used for financing activities	146		(927)
Effect of foreign currency rate changes on cash and restricted cash	(45)		15
Net Increase (Decrease) in cash and restricted cash	763		828
Cash and restricted cash - beginning of period	1,202	[1]	1,989	[2]
Cash and restricted cash - end of period	1,965	[1]	2,817	[2]
Consolidation, Eliminations [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net Cash Provided by (Used in) Operating Activities	(1,090)		(1,860)
Purchases of fixed maturities available for sale	0		0
Purchases of fixed maturities held to maturity	0		0
Purchases of equity securities	0		0
Proceeds From Sale Of Available For Sale Securities Debt Condensed	0		0
Sales of equity securities	0		0
Maturities and redemptions of fixed maturities available for sale	0		0
Maturities and redemptions of fixed maturities held to maturity	0		0
Net change in short-term investments	0		0
Net derivative instruments settlements	0		0
Private equity contribution	0		0
Private equity distribution	0		0
Payments for Other Deposits	0
Payments to Acquire Other Investments			0
Portion one of payments to acquire 22.4% of Huatai Group	0
Capital contribution	1,200		1,110
Other	0		0
Net cash flows used for investing activities	1,200		1,110
Dividends paid on Common Shares	0		0
Common Shares repurchased	0		0
Proceeds from Issuance of Long-term Debt	0		0
Repayments of Long-term Debt			0
Proceeds from issuance of repurchase agreements	0		0
Repayments of repurchase agreements	0		0
Proceeds from share-based compensation plans	0		0
Dividend to Parent Company	1,090		1,860
Advances (to) from affiliates	0		0
Capital contribution	(1,200)		(1,110)
Net proceeds from (payments to) affiliated notional cash pooling program	(123)	[1]	(578)	[2]
Policyholder contract deposits	0		0
Policyholder contract withdrawals	0		0
Net cash flows used for financing activities	(233)		172
Effect of foreign currency rate changes on cash and restricted cash	0		0
Net Increase (Decrease) in cash and restricted cash	(123)		(578)
Cash and restricted cash - beginning of period	0	[1]	(652)	[2]
Cash and restricted cash - end of period	$ (123)	[1]	$ (1,230)	[2]

[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 and December 31, 2019, 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, 2019 and December 31, 2018, the cash balance of one or more entities was negative; however, the overall Pool balances were positive.