Debt (Narrative) (Details) - USD ($) $ in Millions	Dec. 31, 2022	Mar. 31, 2000
Senior Notes | INA Senior Notes Due December 2051 [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 600.0
Long-term debt stated interest rate	2.85%
Senior Notes | INA Senior Notes Due December 2061 [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 1,000.0
Long-term debt stated interest rate	3.05%
Trust Preferred Securities | Chubb INA Capital Securities Due 2030 [Member]
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%