Employee Benefit Plans - PAC - Fair Value Measurements (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
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 | PAC
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	271	264	324
Other Postretirement | PAC | Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	138	132
Other Postretirement | PAC | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	21	18
Other Postretirement | PAC | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	117	114
Other Postretirement | PAC | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Other Postretirement | PAC | Cash equivalents | Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	7	10
Other Postretirement | PAC | Cash equivalents | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	4	5
Other Postretirement | PAC | Cash equivalents | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	3	5
Other Postretirement | PAC | Cash equivalents | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Other Postretirement | PAC | U.S. government obligations | Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	9	6
Other Postretirement | PAC | U.S. government obligations | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	9	6
Other Postretirement | PAC | U.S. government obligations | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Other Postretirement | PAC | U.S. government obligations | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Other Postretirement | PAC | Corporate obligations | Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	45	49
Other Postretirement | PAC | Corporate obligations | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Other Postretirement | PAC | Corporate obligations | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	45	49
Other Postretirement | PAC | Corporate obligations | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Other Postretirement | PAC | Municipal obligations | Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	19	13
Other Postretirement | PAC | Municipal obligations | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Other Postretirement | PAC | Municipal obligations | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	19	13
Other Postretirement | PAC | Municipal obligations | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Other Postretirement | PAC | 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	50	47
Other Postretirement | PAC | 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 | PAC | Agency, asset and mortgage-backed obligations | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	50	47
Other Postretirement | PAC | 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 | PAC | 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 | PAC | 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 | PAC | 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 | PAC | Equity securities, U.S. companies | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	$ 0	$ 0
Other Postretirement | PAC | Investment funds
Defined Benefit Plan Disclosure [Line Items]
Percentage of funds comprised of equity securities	38.00%	41.00%
Percentage of funds comprised of debt securities	62.00%	59.00%
Percentage of funds invested in United States securities	89.00%	91.00%
Percentage of funds invested in international securities	11.00%	9.00%
Other Postretirement | PAC | Investment funds | NAV
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	$ 133	$ 132
U.S. | Pension
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	2,069	2,013	2,795
U.S. | Pension | Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	1,123	1,096
U.S. | Pension | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	319	308
U.S. | Pension | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	804	788
U.S. | Pension | Cash equivalents | Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	40	51
U.S. | Pension | Cash equivalents | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
U.S. | Pension | Cash equivalents | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	40	51
U.S. | Pension | U.S. government obligations | Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	129	109
U.S. | Pension | U.S. government obligations | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	129	109
U.S. | Pension | U.S. government obligations | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
U.S. | Pension | Corporate obligations | Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	620	613
U.S. | Pension | Corporate obligations | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
U.S. | Pension | Corporate obligations | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	620	613
U.S. | Pension | Municipal obligations | Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	40	43
U.S. | Pension | Municipal obligations | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
U.S. | Pension | Municipal obligations | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	40	43
U.S. | Pension | 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	104	81
U.S. | Pension | Agency, asset and mortgage-backed obligations | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
U.S. | Pension | Agency, asset and mortgage-backed obligations | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	104	81
U.S. | Pension | Equity securities, U.S. companies | Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	189	198
U.S. | Pension | Equity securities, U.S. companies | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	189	198
U.S. | Pension | Equity securities, U.S. companies | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	$ 0	$ 0
U.S. | Pension | Investment funds
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%
U.S. | Pension | Investment funds | NAV
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	$ 920	$ 885
U.S. | Pension | Limited partnership interests | NAV
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	26	32
U.S. | Pension | PAC
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	764	758	$ 1,058
U.S. | Pension | PAC | Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	428	380
U.S. | Pension | PAC | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	105	110
U.S. | Pension | PAC | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	323	270
U.S. | Pension | PAC | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
U.S. | Pension | PAC | Cash equivalents | Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	28	10
U.S. | Pension | PAC | Cash equivalents | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
U.S. | Pension | PAC | Cash equivalents | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	28	10
U.S. | Pension | PAC | Cash equivalents | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
U.S. | Pension | PAC | U.S. government obligations | Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	52	41
U.S. | Pension | PAC | U.S. government obligations | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	52	41
U.S. | Pension | PAC | U.S. government obligations | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
U.S. | Pension | PAC | U.S. government obligations | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
U.S. | Pension | PAC | Corporate obligations | Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	232	211
U.S. | Pension | PAC | Corporate obligations | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
U.S. | Pension | PAC | Corporate obligations | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	232	211
U.S. | Pension | PAC | Corporate obligations | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
U.S. | Pension | PAC | Municipal obligations | Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	16	15
U.S. | Pension | PAC | Municipal obligations | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
U.S. | Pension | PAC | Municipal obligations | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	16	15
U.S. | Pension | PAC | Municipal obligations | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
U.S. | Pension | PAC | 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	47	34
U.S. | Pension | PAC | Agency, asset and mortgage-backed obligations | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
U.S. | Pension | PAC | Agency, asset and mortgage-backed obligations | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	47	34
U.S. | Pension | PAC | Agency, asset and mortgage-backed obligations | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
U.S. | Pension | PAC | Equity securities, U.S. companies | Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	53	69
U.S. | Pension | PAC | Equity securities, U.S. companies | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	53	69
U.S. | Pension | PAC | Equity securities, U.S. companies | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
U.S. | Pension | PAC | Equity securities, U.S. companies | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	$ 0	$ 0
U.S. | Pension | PAC | Investment funds
Defined Benefit Plan Disclosure [Line Items]
Percentage of funds comprised of equity securities	41.00%	50.00%
Percentage of funds comprised of debt securities	59.00%	50.00%
Percentage of funds invested in United States securities	88.00%	90.00%
Percentage of funds invested in international securities	12.00%	10.00%
U.S. | Pension | PAC | Investment funds | NAV
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	$ 310	$ 346
U.S. | Pension | PAC | Limited partnership interests | NAV
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	$ 26	$ 32