Employee Postretirement Benefits (Pension Plan Assets of the Principal Plans Measured at fair value) (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Principal Plans
Fair value of plan assets	$ 2,019	$ 2,018
Principal Plans \| Fair Value, Inputs, Level 1
Fair value of plan assets	158	219
Principal Plans \| Fair Value, Inputs, Level 2
Fair value of plan assets	253	226
Principal Plans \| Fair Value, Inputs, Level 3
Fair value of plan assets	230	222
Principal Plans \| Cash and Cash Equivalents
Fair value of plan assets	34	69
Principal Plans \| Cash and Cash Equivalents \| Net Asset Value or Its Equivalent
Fair value of plan assets		76
Principal Plans \| Cash and Cash Equivalents \| Fair Value, Inputs, Level 1
Fair value of plan assets	23	69
Principal Plans \| Cash and Cash Equivalents \| Fair Value, Inputs, Level 2
Fair value of plan assets	11
Principal Plans \| U.S. government and municipals
Fair value of plan assets	98	115
Principal Plans \| U.S. government and municipals \| Net Asset Value or Its Equivalent
Fair value of plan assets	85	71
Principal Plans \| U.S. government and municipals \| Fair Value, Inputs, Level 1
Fair value of plan assets	97	115
Principal Plans \| U.S. government and municipals \| Fair Value, Inputs, Level 2
Fair value of plan assets	1
Principal Plans \| U.S. corporate debt
Fair value of plan assets	203	193
Principal Plans \| U.S. corporate debt \| Net Asset Value or Its Equivalent
Fair value of plan assets	408	419
Principal Plans \| U.S. corporate debt \| Fair Value, Inputs, Level 1
Fair value of plan assets		0
Principal Plans \| U.S. corporate debt \| Fair Value, Inputs, Level 2
Fair value of plan assets	203	193
Principal Plans \| International bonds
Fair value of plan assets	38	33
Principal Plans \| International bonds \| Net Asset Value or Its Equivalent
Fair value of plan assets	591	549
Principal Plans \| International bonds \| Fair Value, Inputs, Level 2
Fair value of plan assets	38	33
Principal Plans \| U.S. Equity
Fair value of plan assets		21
Principal Plans \| U.S. Equity \| Fair Value, Inputs, Level 1
Fair value of plan assets		21
Principal Plans \| International Equity
Fair value of plan assets	15	15
Principal Plans \| International Equity \| Fair Value, Inputs, Level 1
Fair value of plan assets		15
Principal Plans \| Non-U.S. Equity \| Net Asset Value or Its Equivalent
Fair value of plan assets		15
Principal Plans \| Global equity
Fair value of plan assets	224
Principal Plans \| Global equity \| Net Asset Value or Its Equivalent
Fair value of plan assets		221
Principal Plans \| Insurance Contract
Fair value of plan assets	230	222
Principal Plans \| Insurance Contract \| Fair Value, Inputs, Level 3
Fair value of plan assets	230	222
Principal Plans \| Other
Fair value of plan assets	2	(1)
Principal Plans \| Other \| Fair Value, Inputs, Level 1
Fair value of plan assets	2	(1)
Principal Plans \| Defined Benefit Plan, Equity Securities, Non-US
Fair value of plan assets	3
Principal Plans \| Defined Benefit Plan, Equity Securities, Non-US \| Fair Value, Inputs, Level 1
Fair value of plan assets	15
Principal Plans \| Defined Benefit Plan, Equity Securities, US
Fair value of plan assets	21
Principal Plans \| Defined Benefit Plan, Equity Securities, US \| Fair Value, Inputs, Level 1
Fair value of plan assets	21
Principal Plans \| Non-U.S securitized
Fair value of plan assets	67
Defined Benefit Pension Plans
Fair value of plan assets	$ 2,329	$ 2,321	$ 3,744