Postretirement benefits Schedule of Allocation of Plan Assets (Details) - USD ($) $ in Millions	Dec. 31, 2020		Dec. 31, 2019		Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Other Investments	$ 7,945		$ 6,062
Cash	1,747	[1]	1,537	[2]	$ 1,247
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	120		152		143
Fair Value, Recurring [Member] | Level 1
Defined Benefit Plan Disclosure [Line Items]
Other Investments	434		412
Fair Value, Recurring [Member] | Level 2
Defined Benefit Plan Disclosure [Line Items]
Other Investments	438		377
Fair Value, Recurring [Member] | Level 3
Defined Benefit Plan Disclosure [Line Items]
Other Investments	10		10
Other Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Other Investments	60		95
Investment Funds Limited Partnerships Partially Owned Investment Companies Fair Value [Member]
Defined Benefit Plan Disclosure [Line Items]
Other Investments	6,770		4,921
UNITED STATES | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets excluding measured using NAV	3,108		2,873
Defined Benefit Plan, Plan Assets, Amount	3,739		3,301		2,784
Cash	14
UNITED STATES | Pension Plan [Member] | Level 1
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets excluding measured using NAV	2,127		1,951
UNITED STATES | Pension Plan [Member] | Level 2
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets excluding measured using NAV	981		922
UNITED STATES | Pension Plan [Member] | Level 3
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets excluding measured using NAV	0		0
UNITED STATES | Pension Plan [Member] | Short-term investments
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets excluding measured using NAV	59		55
UNITED STATES | Pension Plan [Member] | Short-term investments | Level 1
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets excluding measured using NAV	59		18
UNITED STATES | Pension Plan [Member] | Short-term investments | Level 2
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets excluding measured using NAV	0		37
UNITED STATES | Pension Plan [Member] | Short-term investments | Level 3
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets excluding measured using NAV	0		0
UNITED STATES | Pension Plan [Member] | US Treasury and Government [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets excluding measured using NAV	436		600
UNITED STATES | Pension Plan [Member] | US Treasury and Government [Member] | Level 1
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets excluding measured using NAV	250		466
UNITED STATES | Pension Plan [Member] | US Treasury and Government [Member] | Level 2
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets excluding measured using NAV	186		134
UNITED STATES | Pension Plan [Member] | US Treasury and Government [Member] | Level 3
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets excluding measured using NAV	0		0
UNITED STATES | Pension Plan [Member] | Debt Security, Government, Non-US [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets excluding measured using NAV	793		749
UNITED STATES | Pension Plan [Member] | Debt Security, Government, Non-US [Member] | Level 1
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets excluding measured using NAV	0		0
UNITED STATES | Pension Plan [Member] | Debt Security, Government, Non-US [Member] | Level 2
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets excluding measured using NAV	793		749
UNITED STATES | Pension Plan [Member] | Debt Security, Government, Non-US [Member] | Level 3
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets excluding measured using NAV	0		0
UNITED STATES | Pension Plan [Member] | States, municipalities, and political subdivisions
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets excluding measured using NAV	2		2
UNITED STATES | Pension Plan [Member] | States, municipalities, and political subdivisions | Level 1
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets excluding measured using NAV	0		0
UNITED STATES | Pension Plan [Member] | States, municipalities, and political subdivisions | Level 2
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets excluding measured using NAV	2		2
UNITED STATES | Pension Plan [Member] | States, municipalities, and political subdivisions | Level 3
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets excluding measured using NAV	0		0
UNITED STATES | Pension Plan [Member] | Defined Benefit Plan, Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets excluding measured using NAV	1,818		1,467
UNITED STATES | Pension Plan [Member] | Defined Benefit Plan, Equity Securities [Member] | Level 1
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets excluding measured using NAV	1,818		1,467
UNITED STATES | Pension Plan [Member] | Defined Benefit Plan, Equity Securities [Member] | Level 2
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets excluding measured using NAV	0		0
UNITED STATES | Pension Plan [Member] | Defined Benefit Plan, Equity Securities [Member] | Level 3
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets excluding measured using NAV	0		0
UNITED STATES | Other Investments [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Other Investments	543		428
UNITED STATES | Investment Funds Limited Partnerships Partially Owned Investment Companies Fair Value [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Other Investments	74
Non - U.S. | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets excluding measured using NAV	1,129		1,030
Defined Benefit Plan, Plan Assets, Amount	1,284		1,141		$ 1,008
Non - U.S. | Pension Plan [Member] | Level 1
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets excluding measured using NAV	132		114
Non - U.S. | Pension Plan [Member] | Level 2
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets excluding measured using NAV	997		916
Non - U.S. | Pension Plan [Member] | Level 3
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets excluding measured using NAV	0		0
Non - U.S. | Pension Plan [Member] | Short-term investments
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets excluding measured using NAV	5		2
Non - U.S. | Pension Plan [Member] | Short-term investments | Level 1
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets excluding measured using NAV	5		2
Non - U.S. | Pension Plan [Member] | Short-term investments | Level 2
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets excluding measured using NAV	0		0
Non - U.S. | Pension Plan [Member] | Short-term investments | Level 3
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets excluding measured using NAV	0		0
Non - U.S. | Pension Plan [Member] | Debt Security, Government, Non-US [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets excluding measured using NAV	609		598
Non - U.S. | Pension Plan [Member] | Debt Security, Government, Non-US [Member] | Level 1
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets excluding measured using NAV	0		0
Non - U.S. | Pension Plan [Member] | Debt Security, Government, Non-US [Member] | Level 2
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets excluding measured using NAV	609		598
Non - U.S. | Pension Plan [Member] | Debt Security, Government, Non-US [Member] | Level 3
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets excluding measured using NAV	0		0
Non - U.S. | Pension Plan [Member] | Defined Benefit Plan, Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets excluding measured using NAV	515		430
Non - U.S. | Pension Plan [Member] | Defined Benefit Plan, Equity Securities [Member] | Level 1
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets excluding measured using NAV	127		112
Non - U.S. | Pension Plan [Member] | Defined Benefit Plan, Equity Securities [Member] | Level 2
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets excluding measured using NAV	388		318
Non - U.S. | Pension Plan [Member] | Defined Benefit Plan, Equity Securities [Member] | Level 3
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets excluding measured using NAV	0		0
Non - U.S. | Other Investments [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Other Investments	147		107
Non - U.S. | Investment Funds Limited Partnerships Partially Owned Investment Companies Fair Value [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Other Investments	$ 8		$ 4

[1] Chubb maintains two notional multicurrency cash pools (Pools) with a third-party bank. Refer to Note 1 f) for additional information. At December 31, 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 Note 1 f) for additional information.