Benefit Plans - Other Postretirement Benefit Plan Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
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	81	93	$ 96
Other Postretirement Benefits | Total
Other Postretirement Benefits Plan Assets Measured at Fair Value on a Recurring Basis [Abstract]
Total plan assets		93
Other Postretirement Benefits | Total | Defined Benefit Plan, Assets Before And Other Liabilities
Other Postretirement Benefits Plan Assets Measured at Fair Value on a Recurring Basis [Abstract]
Total plan assets	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	90	70
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	55	31
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	34	32
Other Postretirement Benefits | Total | Asset-backed
Other Postretirement Benefits Plan Assets Measured at Fair Value on a Recurring Basis [Abstract]
Total plan assets	1	7
Other Postretirement Benefits | Total | Short term investments
Other Postretirement Benefits Plan Assets Measured at Fair Value on a Recurring Basis [Abstract]
Total plan assets	2	4
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	19
Other Postretirement Benefits | Total | Other liabilities
Other Postretirement Benefits Plan Assets Measured at Fair Value on a Recurring Basis [Abstract]
Total plan assets	13
Other Postretirement Benefits | Level 1
Other Postretirement Benefits Plan Assets Measured at Fair Value on a Recurring Basis [Abstract]
Total plan assets		23
Other Postretirement Benefits | Level 1 | Defined Benefit Plan, Assets Before And Other Liabilities
Other Postretirement Benefits Plan Assets Measured at Fair Value on a Recurring Basis [Abstract]
Total plan assets	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	2	4
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	19
Other Postretirement Benefits | Level 1 | Other liabilities
Other Postretirement Benefits Plan Assets Measured at Fair Value on a Recurring Basis [Abstract]
Total plan assets	13
Other Postretirement Benefits | Level 2
Other Postretirement Benefits Plan Assets Measured at Fair Value on a Recurring Basis [Abstract]
Total plan assets		70
Other Postretirement Benefits | Level 2 | Defined Benefit Plan, Assets Before And Other Liabilities
Other Postretirement Benefits Plan Assets Measured at Fair Value on a Recurring Basis [Abstract]
Total plan assets	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	90	70
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	55	31
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	34	32
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	7
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
Other Postretirement Benefits Plan Assets Measured at Fair Value on a Recurring Basis [Abstract]
Total plan assets		0
Other Postretirement Benefits | Level 3 | Defined Benefit Plan, Assets Before And Other Liabilities
Other Postretirement Benefits Plan Assets Measured at Fair Value on a Recurring Basis [Abstract]
Total plan assets	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