Employee Benefit Plans - MEC - Fair Value Measurements (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Pension | U.S.
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	$ 2,069	$ 2,013	$ 2,795
Pension | Level 1, 2 and 3 | U.S.
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	1,123	1,096
Pension | Level 1 | U.S.
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	319	308
Pension | Level 2 | U.S.
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	804	788
Pension | Cash equivalents | Level 1, 2 and 3 | U.S.
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	40	51
Pension | Cash equivalents | Level 1 | U.S.
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Pension | Cash equivalents | Level 2 | U.S.
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	40	51
Pension | U.S. government obligations | Level 1, 2 and 3 | U.S.
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	129	109
Pension | U.S. government obligations | Level 1 | U.S.
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	129	109
Pension | U.S. government obligations | Level 2 | U.S.
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Pension | Corporate obligations | Level 1, 2 and 3 | U.S.
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	620	613
Pension | Corporate obligations | Level 1 | U.S.
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Pension | Corporate obligations | Level 2 | U.S.
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	620	613
Pension | Municipal obligations | Level 1, 2 and 3 | U.S.
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	40	43
Pension | Municipal obligations | Level 1 | U.S.
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Pension | Municipal obligations | Level 2 | U.S.
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	40	43
Pension | Agency, asset and mortgage-backed obligations | Level 1, 2 and 3 | U.S.
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	104	81
Pension | Agency, asset and mortgage-backed obligations | Level 1 | U.S.
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Pension | Agency, asset and mortgage-backed obligations | Level 2 | U.S.
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	104	81
Pension | Equity securities, U.S. companies | Level 1, 2 and 3 | U.S.
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	189	198
Pension | Equity securities, U.S. companies | Level 1 | U.S.
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	189	198
Pension | Equity securities, U.S. companies | Level 2 | U.S.
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Pension | Equity securities, international companies | Level 1, 2 and 3 | U.S.
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	1	1
Pension | Equity securities, international companies | Level 1 | U.S.
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	1	1
Pension | Equity securities, international companies | Level 2 | U.S.
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	$ 0	$ 0
Pension | Investment funds | U.S.
Defined Benefit Plan Disclosure [Line Items]
Percentage of funds comprised of equity securities	51.00%	53.00%
Percentage of funds comprised of debt securities	49.00%	47.00%
Percentage of funds invested in United States securities	94.00%	95.00%
Percentage of funds invested in international securities	6.00%	5.00%
Pension | Investment funds | NAV | U.S.
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	$ 920	$ 885
Pension | MEC | U.S.
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	516	490	704
Pension | MEC | Level 1, 2 and 3 | U.S.
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	232	267
Pension | MEC | Level 1 | U.S.
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	91	94
Pension | MEC | Level 2 | U.S.
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	141	173
Pension | MEC | Level 3 | U.S.
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Pension | MEC | Cash equivalents | Level 1, 2 and 3 | U.S.
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	11	15
Pension | MEC | Cash equivalents | Level 1 | U.S.
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Pension | MEC | Cash equivalents | Level 2 | U.S.
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	11	15
Pension | MEC | Cash equivalents | Level 3 | U.S.
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Pension | MEC | U.S. government obligations | Level 1, 2 and 3 | U.S.
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	25	22
Pension | MEC | U.S. government obligations | Level 1 | U.S.
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	25	22
Pension | MEC | U.S. government obligations | Level 2 | U.S.
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Pension | MEC | U.S. government obligations | Level 3 | U.S.
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Pension | MEC | Corporate obligations | Level 1, 2 and 3 | U.S.
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	110	135
Pension | MEC | Corporate obligations | Level 1 | U.S.
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Pension | MEC | Corporate obligations | Level 2 | U.S.
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	110	135
Pension | MEC | Corporate obligations | Level 3 | U.S.
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Pension | MEC | Municipal obligations | Level 1, 2 and 3 | U.S.
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	6	10
Pension | MEC | Municipal obligations | Level 1 | U.S.
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Pension | MEC | Municipal obligations | Level 2 | U.S.
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	6	10
Pension | MEC | Municipal obligations | Level 3 | U.S.
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Pension | MEC | Agency, asset and mortgage-backed obligations | Level 1, 2 and 3 | U.S.
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	14	13
Pension | MEC | Agency, asset and mortgage-backed obligations | Level 1 | U.S.
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Pension | MEC | Agency, asset and mortgage-backed obligations | Level 2 | U.S.
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	14	13
Pension | MEC | Agency, asset and mortgage-backed obligations | Level 3 | U.S.
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Pension | MEC | Equity securities, U.S. companies | Level 1, 2 and 3 | U.S.
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	65	71
Pension | MEC | Equity securities, U.S. companies | Level 1 | U.S.
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	65	71
Pension | MEC | Equity securities, U.S. companies | Level 2 | U.S.
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Pension | MEC | Equity securities, U.S. companies | Level 3 | U.S.
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Pension | MEC | Equity securities, international companies | Level 1, 2 and 3 | U.S.
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	1	1
Pension | MEC | Equity securities, international companies | Level 1 | U.S.
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	1	1
Pension | MEC | Equity securities, international companies | Level 2 | U.S.
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Pension | MEC | Equity securities, international companies | Level 3 | U.S.
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	$ 0	$ 0
Pension | MEC | Investment funds | U.S.
Defined Benefit Plan Disclosure [Line Items]
Percentage of funds comprised of equity securities	68.00%	55.00%
Percentage of funds comprised of debt securities	32.00%	45.00%
Percentage of funds invested in United States securities	93.00%	97.00%
Percentage of funds invested in international securities	7.00%	3.00%
Pension | MEC | Investment funds | NAV | U.S.
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	$ 284	$ 223
Other Postretirement
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	665	614	769
Other Postretirement | Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	532	482
Other Postretirement | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	372	337
Other Postretirement | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	160	145
Other Postretirement | Cash equivalents | Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	22	24
Other Postretirement | Cash equivalents | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	13	15
Other Postretirement | Cash equivalents | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	9	9
Other Postretirement | U.S. government obligations | Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	11	8
Other Postretirement | U.S. government obligations | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	11	8
Other Postretirement | U.S. government obligations | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Other Postretirement | Corporate obligations | Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	50	52
Other Postretirement | Corporate obligations | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Other Postretirement | Corporate obligations | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	50	52
Other Postretirement | Municipal obligations | Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	45	35
Other Postretirement | Municipal obligations | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Other Postretirement | Municipal obligations | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	45	35
Other Postretirement | Agency, asset and mortgage-backed obligations | Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	56	49
Other Postretirement | Agency, asset and mortgage-backed obligations | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Other Postretirement | Agency, asset and mortgage-backed obligations | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	56	49
Other Postretirement | Equity securities, U.S. companies | Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	8	7
Other Postretirement | Equity securities, U.S. companies | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	8	7
Other Postretirement | Equity securities, U.S. companies | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	$ 0	$ 0
Other Postretirement | Investment funds
Defined Benefit Plan Disclosure [Line Items]
Percentage of funds comprised of equity securities	55.00%	55.00%
Percentage of funds comprised of debt securities	45.00%	45.00%
Percentage of funds invested in United States securities	88.00%	88.00%
Percentage of funds invested in international securities	12.00%	12.00%
Other Postretirement | Investment funds | Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	$ 340	$ 307
Other Postretirement | Investment funds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	340	307
Other Postretirement | Investment funds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Other Postretirement | Investment funds | NAV
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	133	132
Other Postretirement | MEC
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	278	240	$ 308
Other Postretirement | MEC | Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	278	240
Other Postretirement | MEC | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	241	213
Other Postretirement | MEC | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	37	27
Other Postretirement | MEC | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Other Postretirement | MEC | Cash equivalents | Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	9	10
Other Postretirement | MEC | Cash equivalents | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	9	10
Other Postretirement | MEC | Cash equivalents | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Other Postretirement | MEC | Cash equivalents | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Other Postretirement | MEC | U.S. government obligations | Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	2	2
Other Postretirement | MEC | U.S. government obligations | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	2	2
Other Postretirement | MEC | U.S. government obligations | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Other Postretirement | MEC | U.S. government obligations | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Other Postretirement | MEC | Corporate obligations | Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	5	3
Other Postretirement | MEC | Corporate obligations | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Other Postretirement | MEC | Corporate obligations | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	5	3
Other Postretirement | MEC | Corporate obligations | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Other Postretirement | MEC | Municipal obligations | Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	26	22
Other Postretirement | MEC | Municipal obligations | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Other Postretirement | MEC | Municipal obligations | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	26	22
Other Postretirement | MEC | Municipal obligations | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Other Postretirement | MEC | Agency, asset and mortgage-backed obligations | Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	6	2
Other Postretirement | MEC | Agency, asset and mortgage-backed obligations | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Other Postretirement | MEC | Agency, asset and mortgage-backed obligations | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	6	2
Other Postretirement | MEC | Agency, asset and mortgage-backed obligations | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	$ 0	$ 0
Other Postretirement | MEC | Investment funds
Defined Benefit Plan Disclosure [Line Items]
Percentage of funds comprised of equity securities	83.00%	82.00%
Percentage of funds comprised of debt securities	17.00%	18.00%
Percentage of funds invested in United States securities	83.00%	82.00%
Percentage of funds invested in international securities	17.00%	18.00%
Other Postretirement | MEC | Investment funds | Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	$ 230	$ 201
Other Postretirement | MEC | Investment funds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	230	201
Other Postretirement | MEC | Investment funds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Other Postretirement | MEC | Investment funds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	$ 0	$ 0