Debt (Schedule of debt instruments) (Details) - USD ($)	Dec. 31, 2023	Dec. 31, 2022
Debt Instrument [Line Items]
Short-term debt	$ 550,000,000	$ 243,000,000	[1]
Long-term debt	2,481,000,000	2,538,000,000	[1]
Total debt	$ 3,031,000,000	2,781,000,000
3.950%, face amount of $550, due May 15, 2024
Debt Instrument [Line Items]
Stated interest rate	3.95%
Face amount	$ 550,000,000
Long-term debt	$ 0	549,000,000
4.500%, face amount of $500, due March 1, 2026
Debt Instrument [Line Items]
Stated interest rate	4.50%
Face amount	$ 500,000,000
Long-term debt	$ 500,000,000	499,000,000
3.450%, face amount of $500, due August 15, 2027
Debt Instrument [Line Items]
Stated interest rate	3.45%
Face amount	$ 500,000,000
Long-term debt	$ 498,000,000	497,000,000
3.900%, face amount of $500, due May 1, 2029
Debt Instrument [Line Items]
Stated interest rate	3.90%
Face amount	$ 500,000,000
Long-term debt	$ 497,000,000	497,000,000
2.050%, face amount of $500, due August 15, 2030
Debt Instrument [Line Items]
Stated interest rate	2.05%
Face amount	$ 500,000,000
Long-term debt	$ 496,000,000	496,000,000
5.500%, face amount of $500, due June 15, 2033
Debt Instrument [Line Items]
Stated interest rate	5.50%
Face amount	$ 500,000,000
Long-term debt	$ 490,000,000	0
Debenture of CNAF, 7.250%, face amount of $243, due November 15, 2023
Debt Instrument [Line Items]
Stated interest rate	7.25%
Face amount	$ 243,000,000
Short-term debt	0	243,000,000
3.950%, face amount of $550, due May 15, 2024
Debt Instrument [Line Items]
Short-term debt	$ 550,000,000	$ 0

[1] As of January 1, 2023, the Company adopted ASU 2018-12, Financial Services-Insurance (Topic 944): Targeted Improvements to the Accounting for Long-Duration Contracts (ASU 2018-12) using the modified retrospective method applied as of the transition date of January 1, 2021. Prior period amounts in the financial statements have been adjusted to reflect application of the new guidance. See Note A to the Consolidated Financial Statements for additional information.