Pension Plans, Retirement Benefits and Savings Plans (Details) - Fair Value - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	$ 4,246	$ 4,033	$ 5,036
Pension Plans [Member] | Level 1 [Member]
Defined benefit plan disclosure
Fair value of plan assets	3,272	3,149
Pension Plans [Member] | Level 2 [Member]
Defined benefit plan disclosure
Fair value of plan assets	973	883
Pension Plans [Member] | Level 3 [Member]
Defined benefit plan disclosure
Fair value of plan assets	1	1
Pension Plans [Member] | Fixed maturities [Member]
Defined benefit plan disclosure
Fair value of plan assets	921	822
Pension Plans [Member] | Fixed maturities [Member] | Level 1 [Member]
Defined benefit plan disclosure
Fair value of plan assets	0	0
Pension Plans [Member] | Fixed maturities [Member] | Level 2 [Member]
Defined benefit plan disclosure
Fair value of plan assets	921	822
Pension Plans [Member] | Fixed maturities [Member] | Level 3 [Member]
Defined benefit plan disclosure
Fair value of plan assets	0	0
Pension Plans [Member] | Obligations of U.S. states, municipalities and political subdivisions [Member]
Defined benefit plan disclosure
Fair value of plan assets	105	80
Pension Plans [Member] | Obligations of U.S. states, municipalities and political subdivisions [Member] | Level 1 [Member]
Defined benefit plan disclosure
Fair value of plan assets	0	0
Pension Plans [Member] | Obligations of U.S. states, municipalities and political subdivisions [Member] | Level 2 [Member]
Defined benefit plan disclosure
Fair value of plan assets	105	80
Pension Plans [Member] | Obligations of U.S. states, municipalities and political subdivisions [Member] | Level 3 [Member]
Defined benefit plan disclosure
Fair value of plan assets	0	0
Pension Plans [Member] | Debt securities issued by foreign governments [Member]
Defined benefit plan disclosure
Fair value of plan assets	32	25
Pension Plans [Member] | Debt securities issued by foreign governments [Member] | Level 1 [Member]
Defined benefit plan disclosure
Fair value of plan assets	0	0
Pension Plans [Member] | Debt securities issued by foreign governments [Member] | Level 2 [Member]
Defined benefit plan disclosure
Fair value of plan assets	32	25
Pension Plans [Member] | Debt securities issued by foreign governments [Member] | Level 3 [Member]
Defined benefit plan disclosure
Fair value of plan assets	0	0
Pension Plans [Member] | Mortgage-backed securities, collateralized mortgage obligations and pass-through securities [Member]
Defined benefit plan disclosure
Fair value of plan assets	8	4
Pension Plans [Member] | Mortgage-backed securities, collateralized mortgage obligations and pass-through securities [Member] | Level 1 [Member]
Defined benefit plan disclosure
Fair value of plan assets	0	0
Pension Plans [Member] | Mortgage-backed securities, collateralized mortgage obligations and pass-through securities [Member] | Level 2 [Member]
Defined benefit plan disclosure
Fair value of plan assets	8	4
Pension Plans [Member] | Mortgage-backed securities, collateralized mortgage obligations and pass-through securities [Member] | Level 3 [Member]
Defined benefit plan disclosure
Fair value of plan assets	0	0
Pension Plans [Member] | Corporate and all other bonds [Member]
Defined benefit plan disclosure
Fair value of plan assets	776	713
Pension Plans [Member] | Corporate and all other bonds [Member] | Level 1 [Member]
Defined benefit plan disclosure
Fair value of plan assets	0	0
Pension Plans [Member] | Corporate and all other bonds [Member] | Level 2 [Member]
Defined benefit plan disclosure
Fair value of plan assets	776	713
Pension Plans [Member] | Corporate and all other bonds [Member] | Level 3 [Member]
Defined benefit plan disclosure
Fair value of plan assets	0	0
Pension Plans [Member] | Total mutual funds [Member]
Defined benefit plan disclosure
Fair value of plan assets	1,865	1,911
Pension Plans [Member] | Total mutual funds [Member] | Level 1 [Member]
Defined benefit plan disclosure
Fair value of plan assets	1,856	1,902
Pension Plans [Member] | Total mutual funds [Member] | Level 2 [Member]
Defined benefit plan disclosure
Fair value of plan assets	9	9
Pension Plans [Member] | Total mutual funds [Member] | Level 3 [Member]
Defined benefit plan disclosure
Fair value of plan assets	0	0
Pension Plans [Member] | Equity mutual funds [Member]
Defined benefit plan disclosure
Fair value of plan assets	1,207	1,157
Pension Plans [Member] | Equity mutual funds [Member] | Level 1 [Member]
Defined benefit plan disclosure
Fair value of plan assets	1,201	1,151
Pension Plans [Member] | Equity mutual funds [Member] | Level 2 [Member]
Defined benefit plan disclosure
Fair value of plan assets	6	6
Pension Plans [Member] | Equity mutual funds [Member] | Level 3 [Member]
Defined benefit plan disclosure
Fair value of plan assets	0	0
Pension Plans [Member] | Bond mutual funds [Member]
Defined benefit plan disclosure
Fair value of plan assets	658	754
Pension Plans [Member] | Bond mutual funds [Member] | Level 1 [Member]
Defined benefit plan disclosure
Fair value of plan assets	655	751
Pension Plans [Member] | Bond mutual funds [Member] | Level 2 [Member]
Defined benefit plan disclosure
Fair value of plan assets	3	3
Pension Plans [Member] | Bond mutual funds [Member] | Level 3 [Member]
Defined benefit plan disclosure
Fair value of plan assets	0	0
Pension Plans [Member] | Equity securities [Member]
Defined benefit plan disclosure
Fair value of plan assets	1,302	1,116
Pension Plans [Member] | Equity securities [Member] | Level 1 [Member]
Defined benefit plan disclosure
Fair value of plan assets	1,302	1,116
Pension Plans [Member] | Equity securities [Member] | Level 2 [Member]
Defined benefit plan disclosure
Fair value of plan assets	0	0
Pension Plans [Member] | Equity securities [Member] | Level 3 [Member]
Defined benefit plan disclosure
Fair value of plan assets	0	0
Pension Plans [Member] | Other investments [Member]
Defined benefit plan disclosure
Fair value of plan assets	1	1
Pension Plans [Member] | Other investments [Member] | Level 1 [Member]
Defined benefit plan disclosure
Fair value of plan assets	0	0
Pension Plans [Member] | Other investments [Member] | Level 2 [Member]
Defined benefit plan disclosure
Fair value of plan assets	0	0
Pension Plans [Member] | Other investments [Member] | Level 3 [Member]
Defined benefit plan disclosure
Fair value of plan assets	1	1
Pension Plans [Member] | Cash and short-term securities [Member]
Defined benefit plan disclosure
Fair value of plan assets	157	183
Pension Plans [Member] | Cash and short-term securities [Member] | Level 1 [Member]
Defined benefit plan disclosure
Fair value of plan assets	114	131
Pension Plans [Member] | Cash and short-term securities [Member] | Level 2 [Member]
Defined benefit plan disclosure
Fair value of plan assets	43	52
Pension Plans [Member] | Cash and short-term securities [Member] | Level 3 [Member]
Defined benefit plan disclosure
Fair value of plan assets	0	0
Pension Plans [Member] | Cash and short-term securities, U.S. Treasury securities [Member]
Defined benefit plan disclosure
Fair value of plan assets	0	0
Pension Plans [Member] | Cash and short-term securities, U.S. Treasury securities [Member] | Level 1 [Member]
Defined benefit plan disclosure
Fair value of plan assets	0	0
Pension Plans [Member] | Cash and short-term securities, U.S. Treasury securities [Member] | Level 2 [Member]
Defined benefit plan disclosure
Fair value of plan assets	0	0
Pension Plans [Member] | Cash and short-term securities, U.S. Treasury securities [Member] | Level 3 [Member]
Defined benefit plan disclosure
Fair value of plan assets	0	0
Pension Plans [Member] | Cash and short-term securities, other [Member]
Defined benefit plan disclosure
Fair value of plan assets	157	183
Pension Plans [Member] | Cash and short-term securities, other [Member] | Level 1 [Member]
Defined benefit plan disclosure
Fair value of plan assets	114	131
Pension Plans [Member] | Cash and short-term securities, other [Member] | Level 2 [Member]
Defined benefit plan disclosure
Fair value of plan assets	43	52
Pension Plans [Member] | Cash and short-term securities, other [Member] | Level 3 [Member]
Defined benefit plan disclosure
Fair value of plan assets	0	0
Postretirement Benefit Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	7	8	$ 9
Postretirement Benefit Plans [Member] | Level 2 [Member]
Defined benefit plan disclosure
Fair value of plan assets	$ 7	$ 8