Debt (Narrative) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Mar. 31, 2000
INA Senior Notes Due November 2020 [Member] \| Senior Notes
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 1,300.0
Long-term debt stated interest rate	2.30%
Senior Notes \| INA Senior Notes Due September 2030
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 1,000.0
Long-term debt stated interest rate	1.375%
Trust Preferred Securities \| INA capital securities due 2030
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 309.0	$ 300.0
ACE Capital Trust II common securities purchased		$ 9.2
Long-term debt stated interest rate	9.70%	9.70%
Unsecured Debt \| INA Senior Notes Due August 2029 [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 100.0
Long-term debt stated interest rate	8.875%

The value of the shares of ACE Capital Trust II purchased by ACE INA.

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Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
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Contractual interest rate for funds borrowed, under the debt agreement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
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+ References

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