Fair Value - Financial Assets and Liabilities not Measured at Fair Value (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Carrying Amount
Assets:
Other invested assets, primarily mortgage loans	$ 1,029	$ 1,035
Liabilities:
Short-term debt	1,677	1,083
Long-term debt	8,422	7,915
Estimated Fair Value
Assets:
Other invested assets, primarily mortgage loans	987	997
Liabilities:
Short-term debt	1,664	1,066
Long-term debt	8,094	7,640
Estimated Fair Value | Level 1
Assets:
Other invested assets, primarily mortgage loans
Liabilities:
Short-term debt
Long-term debt
Estimated Fair Value | Level 2
Assets:
Other invested assets, primarily mortgage loans
Liabilities:
Short-term debt	1,145	546
Long-term debt	7,663	7,255
Estimated Fair Value | Level 3
Assets:
Other invested assets, primarily mortgage loans	987	997
Liabilities:
Short-term debt	519	520
Long-term debt	$ 431	$ 385