Employee Benefit Plans - PAC - Fair Value Measurements (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Other Postretirement
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	$ 769	$ 744	$ 742
Other Postretirement | Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	607	573
Other Postretirement | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	437	340
Other Postretirement | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	170	233
Other Postretirement | Cash equivalents | Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	16	22
Other Postretirement | Cash equivalents | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	12	20
Other Postretirement | Cash equivalents | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	4	2
Other Postretirement | United States government obligations | Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	27	15
Other Postretirement | United States government obligations | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	27	15
Other Postretirement | United States 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	85	102
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	85	102
Other Postretirement | Municipal obligations | Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	43	82
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	43	82
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	38	47
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	38	47
Other Postretirement | Equity securities, United States companies | Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	4	6
Other Postretirement | Equity securities, United States companies | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	4	6
Other Postretirement | Equity securities, United States 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%	40.00%
Percentage of funds comprised of debt securities	45.00%	60.00%
Percentage of funds invested in United States securities	88.00%	79.00%
Percentage of funds invested in international securities	12.00%	21.00%
Other Postretirement | Investment funds | Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	$ 394	$ 299
Other Postretirement | Investment funds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	394	299
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	161	167
Other Postretirement | Limited partnership interests | NAV
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	1	4
Other Postretirement | PAC
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	324	327	334
Other Postretirement | PAC | Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	162	170
Other Postretirement | PAC | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	32	23
Other Postretirement | PAC | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	130	147
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	5	9
Other Postretirement | PAC | Cash equivalents | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	4	8
Other Postretirement | PAC | Cash equivalents | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	1	1
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 | United States government obligations | Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	24	11
Other Postretirement | PAC | United States government obligations | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	24	11
Other Postretirement | PAC | United States government obligations | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Other Postretirement | PAC | United States 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	79	86
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	79	86
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	15	16
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	15	16
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	35	44
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	35	44
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, United States companies | Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	4	4
Other Postretirement | PAC | Equity securities, United States companies | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	4	4
Other Postretirement | PAC | Equity securities, United States companies | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Other Postretirement | PAC | Equity securities, United States 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	39.00%	38.00%
Percentage of funds comprised of debt securities	61.00%	62.00%
Percentage of funds invested in United States securities	90.00%	93.00%
Percentage of funds invested in international securities	10.00%	7.00%
Other Postretirement | PAC | Investment funds | NAV
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	$ 161	$ 153
Other Postretirement | PAC | Limited partnership interests | NAV
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	1	4
United States | Pension
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	2,795	2,824	2,656
United States | Pension | Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	1,412	1,172
United States | Pension | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	277	276
United States | Pension | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	1,135	896
United States | Pension | Cash equivalents | Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	64	79
United States | Pension | Cash equivalents | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
United States | Pension | Cash equivalents | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	64	79
United States | Pension | United States government obligations | Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	142	52
United States | Pension | United States government obligations | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	142	52
United States | Pension | United States government obligations | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
United States | Pension | Corporate obligations | Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	912	748
United States | Pension | Corporate obligations | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
United States | Pension | Corporate obligations | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	912	748
United States | Pension | Municipal obligations | Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	66	69
United States | Pension | Municipal obligations | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
United States | Pension | Municipal obligations | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	66	69
United States | 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	93
United States | Pension | Agency, asset and mortgage-backed obligations | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0
United States | Pension | Agency, asset and mortgage-backed obligations | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	93
United States | Pension | Equity securities, United States companies | Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	135	224
United States | Pension | Equity securities, United States companies | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	135	224
United States | Pension | Equity securities, United States companies | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	$ 0	$ 0
United States | Pension | Investment funds
Defined Benefit Plan Disclosure [Line Items]
Percentage of funds comprised of equity securities	54.00%	69.00%
Percentage of funds comprised of debt securities	46.00%	31.00%
Percentage of funds invested in United States securities	89.00%	79.00%
Percentage of funds invested in international securities	11.00%	21.00%
United States | Pension | Investment funds | NAV
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	$ 1,349	$ 1,521
United States | Pension | Limited partnership interests | NAV
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	34	88
United States | Pension | PAC
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	1,058	1,064	$ 1,036
United States | Pension | PAC | Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	486	389
United States | Pension | PAC | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	112	105
United States | Pension | PAC | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	374	284
United States | Pension | PAC | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
United States | Pension | PAC | Cash equivalents | Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	15	32
United States | Pension | PAC | Cash equivalents | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
United States | Pension | PAC | Cash equivalents | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	15	32
United States | Pension | PAC | Cash equivalents | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
United States | Pension | PAC | United States government obligations | Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	51	14
United States | Pension | PAC | United States government obligations | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	51	14
United States | Pension | PAC | United States government obligations | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
United States | Pension | PAC | United States government obligations | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
United States | Pension | PAC | International government obligations | Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year		0
United States | Pension | PAC | International government obligations | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year		0
United States | Pension | PAC | International government obligations | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year		0
United States | Pension | PAC | International government obligations | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year		0
United States | Pension | PAC | Corporate obligations | Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	299	231
United States | Pension | PAC | Corporate obligations | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
United States | Pension | PAC | Corporate obligations | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	299	231
United States | Pension | PAC | Corporate obligations | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
United States | Pension | PAC | Municipal obligations | Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	22	21
United States | Pension | PAC | Municipal obligations | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
United States | Pension | PAC | Municipal obligations | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	22	21
United States | Pension | PAC | Municipal obligations | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
United States | 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	38
United States | 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
United States | Pension | PAC | Agency, asset and mortgage-backed obligations | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	38
United States | 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
United States | Pension | PAC | Equity securities, United States companies | Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	61	91
United States | Pension | PAC | Equity securities, United States companies | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	61	91
United States | Pension | PAC | Equity securities, United States companies | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
United States | Pension | PAC | Equity securities, United States companies | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	$ 0	$ 0
United States | Pension | PAC | Investment funds
Defined Benefit Plan Disclosure [Line Items]
Percentage of funds comprised of equity securities	59.00%	78.00%
Percentage of funds comprised of debt securities	41.00%	22.00%
Percentage of funds invested in United States securities	84.00%	74.00%
Percentage of funds invested in international securities	16.00%	26.00%
United States | Pension | PAC | Investment funds | NAV
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	$ 538	$ 587
United States | Pension | PAC | Limited partnership interests | NAV
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	$ 34	$ 88