Benefit Plans - Other Postretirement Benefit Plan Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Level 3
Other Postretirement Benefits Plan Assets Measured at Fair Value on a Recurring Basis [Abstract]
Total plan assets	$ 0	$ 0
Other Postretirement Benefits
Other Postretirement Benefits Plan Assets Measured at Fair Value on a Recurring Basis [Abstract]
Total plan assets	83	81	$ 93
Other Postretirement Benefits | Total | Total assets
Other Postretirement Benefits Plan Assets Measured at Fair Value on a Recurring Basis [Abstract]
Total plan assets	122	94
Other Postretirement Benefits | Total | Total fixed maturities
Other Postretirement Benefits Plan Assets Measured at Fair Value on a Recurring Basis [Abstract]
Total plan assets	107	90
Other Postretirement Benefits | Total | Corporate bonds and other
Other Postretirement Benefits Plan Assets Measured at Fair Value on a Recurring Basis [Abstract]
Total plan assets	67	55
Other Postretirement Benefits | Total | States, municipalities and political subdivisions
Other Postretirement Benefits Plan Assets Measured at Fair Value on a Recurring Basis [Abstract]
Total plan assets	39	34
Other Postretirement Benefits | Total | Asset-backed
Other Postretirement Benefits Plan Assets Measured at Fair Value on a Recurring Basis [Abstract]
Total plan assets	1	1
Other Postretirement Benefits | Total | Short-term investments
Other Postretirement Benefits Plan Assets Measured at Fair Value on a Recurring Basis [Abstract]
Total plan assets	13	2
Other Postretirement Benefits | Total | Fixed income mutual funds
Other Postretirement Benefits Plan Assets Measured at Fair Value on a Recurring Basis [Abstract]
Total plan assets	2	2
Other Postretirement Benefits | Total | Other liabilities
Other Postretirement Benefits Plan Assets Measured at Fair Value on a Recurring Basis [Abstract]
Total plan assets	(39)	(13)
Other Postretirement Benefits | Level 1 | Total assets
Other Postretirement Benefits Plan Assets Measured at Fair Value on a Recurring Basis [Abstract]
Total plan assets	15	4
Other Postretirement Benefits | Level 1 | Total fixed maturities
Other Postretirement Benefits Plan Assets Measured at Fair Value on a Recurring Basis [Abstract]
Total plan assets	0	0
Other Postretirement Benefits | Level 1 | Corporate bonds and other
Other Postretirement Benefits Plan Assets Measured at Fair Value on a Recurring Basis [Abstract]
Total plan assets
Other Postretirement Benefits | Level 1 | States, municipalities and political subdivisions
Other Postretirement Benefits Plan Assets Measured at Fair Value on a Recurring Basis [Abstract]
Total plan assets
Other Postretirement Benefits | Level 1 | Asset-backed
Other Postretirement Benefits Plan Assets Measured at Fair Value on a Recurring Basis [Abstract]
Total plan assets
Other Postretirement Benefits | Level 1 | Short-term investments
Other Postretirement Benefits Plan Assets Measured at Fair Value on a Recurring Basis [Abstract]
Total plan assets	13	2
Other Postretirement Benefits | Level 1 | Fixed income mutual funds
Other Postretirement Benefits Plan Assets Measured at Fair Value on a Recurring Basis [Abstract]
Total plan assets	2	2
Other Postretirement Benefits | Level 1 | Other liabilities
Other Postretirement Benefits Plan Assets Measured at Fair Value on a Recurring Basis [Abstract]
Total plan assets	(39)	(13)
Other Postretirement Benefits | Level 2 | Total assets
Other Postretirement Benefits Plan Assets Measured at Fair Value on a Recurring Basis [Abstract]
Total plan assets	107	90
Other Postretirement Benefits | Level 2 | Total fixed maturities
Other Postretirement Benefits Plan Assets Measured at Fair Value on a Recurring Basis [Abstract]
Total plan assets	107	90
Other Postretirement Benefits | Level 2 | Corporate bonds and other
Other Postretirement Benefits Plan Assets Measured at Fair Value on a Recurring Basis [Abstract]
Total plan assets	67	55
Other Postretirement Benefits | Level 2 | States, municipalities and political subdivisions
Other Postretirement Benefits Plan Assets Measured at Fair Value on a Recurring Basis [Abstract]
Total plan assets	39	34
Other Postretirement Benefits | Level 2 | Asset-backed
Other Postretirement Benefits Plan Assets Measured at Fair Value on a Recurring Basis [Abstract]
Total plan assets	1	1
Other Postretirement Benefits | Level 2 | Short-term investments
Other Postretirement Benefits Plan Assets Measured at Fair Value on a Recurring Basis [Abstract]
Total plan assets
Other Postretirement Benefits | Level 2 | Fixed income mutual funds
Other Postretirement Benefits Plan Assets Measured at Fair Value on a Recurring Basis [Abstract]
Total plan assets
Other Postretirement Benefits | Level 2 | Other liabilities
Other Postretirement Benefits Plan Assets Measured at Fair Value on a Recurring Basis [Abstract]
Total plan assets
Other Postretirement Benefits | Level 3 | Total assets
Other Postretirement Benefits Plan Assets Measured at Fair Value on a Recurring Basis [Abstract]
Total plan assets	0	0
Other Postretirement Benefits | Level 3 | Total fixed maturities
Other Postretirement Benefits Plan Assets Measured at Fair Value on a Recurring Basis [Abstract]
Total plan assets	0	0
Other Postretirement Benefits | Level 3 | Corporate bonds and other
Other Postretirement Benefits Plan Assets Measured at Fair Value on a Recurring Basis [Abstract]
Total plan assets
Other Postretirement Benefits | Level 3 | States, municipalities and political subdivisions
Other Postretirement Benefits Plan Assets Measured at Fair Value on a Recurring Basis [Abstract]
Total plan assets
Other Postretirement Benefits | Level 3 | Asset-backed
Other Postretirement Benefits Plan Assets Measured at Fair Value on a Recurring Basis [Abstract]
Total plan assets
Other Postretirement Benefits | Level 3 | Short-term investments
Other Postretirement Benefits Plan Assets Measured at Fair Value on a Recurring Basis [Abstract]
Total plan assets
Other Postretirement Benefits | Level 3 | Fixed income mutual funds
Other Postretirement Benefits Plan Assets Measured at Fair Value on a Recurring Basis [Abstract]
Total plan assets
Other Postretirement Benefits | Level 3 | Other liabilities
Other Postretirement Benefits Plan Assets Measured at Fair Value on a Recurring Basis [Abstract]
Total plan assets