Employee Benefit Plans - MEC - Fair Value Measurements (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Pension | United States
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	$ 2,795	$ 2,824	$ 2,656
Pension | Level 1, 2 and 3 | United States
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	1,412	1,172
Pension | Level 1 | United States
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	277	276
Pension | Level 2 | United States
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	1,135	896
Pension | Cash equivalents | Level 1, 2 and 3 | United States
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	64	79
Pension | Cash equivalents | Level 1 | United States
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Pension | Cash equivalents | Level 2 | United States
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	64	79
Pension | United States government obligations | Level 1, 2 and 3 | United States
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	142	52
Pension | United States government obligations | Level 1 | United States
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	142	52
Pension | United States government obligations | Level 2 | United States
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Pension | Corporate obligations | Level 1, 2 and 3 | United States
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	912	748
Pension | Corporate obligations | Level 1 | United States
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Pension | Corporate obligations | Level 2 | United States
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	912	748
Pension | Municipal obligations | Level 1, 2 and 3 | United States
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	66	69
Pension | Municipal obligations | Level 1 | United States
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Pension | Municipal obligations | Level 2 | United States
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	66	69
Pension | Agency, asset and mortgage-backed obligations | Level 1, 2 and 3 | United States
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	93
Pension | Agency, asset and mortgage-backed obligations | Level 1 | United States
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0
Pension | Agency, asset and mortgage-backed obligations | Level 2 | United States
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	93
Pension | Equity securities, United States companies | Level 1, 2 and 3 | United States
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	135	224
Pension | Equity securities, United States companies | Level 1 | United States
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	135	224
Pension | Equity securities, United States companies | Level 2 | United States
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	$ 0	$ 0
Pension | Investment funds | United States
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%
Pension | Investment funds | NAV | United States
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	$ 1,349	$ 1,521
Pension | Real estate funds | NAV | United States
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year		43
Pension | MEC | United States
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	704	718	717
Pension | MEC | Level 1, 2 and 3 | United States
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	372	282
Pension | MEC | Level 1 | United States
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	68	79
Pension | MEC | Level 2 | United States
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	304	203
Pension | MEC | Level 3 | United States
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 | United States
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	27	26
Pension | MEC | Cash equivalents | Level 1 | United States
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Pension | MEC | Cash equivalents | Level 2 | United States
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	27	26
Pension | MEC | Cash equivalents | Level 3 | United States
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Pension | MEC | United States government obligations | Level 1, 2 and 3 | United States
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	33	14
Pension | MEC | United States government obligations | Level 1 | United States
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	33	14
Pension | MEC | United States government obligations | Level 2 | United States
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Pension | MEC | United States government obligations | Level 3 | United States
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Pension | MEC | International government obligations | Level 1, 2 and 3 | United States
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Pension | MEC | International government obligations | Level 1 | United States
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Pension | MEC | International government obligations | Level 2 | United States
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Pension | MEC | International government obligations | Level 3 | United States
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 | United States
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	242	160
Pension | MEC | Corporate obligations | Level 1 | United States
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Pension | MEC | Corporate obligations | Level 2 | United States
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	242	160
Pension | MEC | Corporate obligations | Level 3 | United States
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 | United States
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	18	17
Pension | MEC | Municipal obligations | Level 1 | United States
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Pension | MEC | Municipal obligations | Level 2 | United States
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	18	17
Pension | MEC | Municipal obligations | Level 3 | United States
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 | United States
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	17	0
Pension | MEC | Agency, asset and mortgage-backed obligations | Level 1 | United States
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 | United States
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	17	0
Pension | MEC | Agency, asset and mortgage-backed obligations | Level 3 | United States
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Pension | MEC | Equity securities, United States companies | Level 1, 2 and 3 | United States
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	35	65
Pension | MEC | Equity securities, United States companies | Level 1 | United States
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	35	65
Pension | MEC | Equity securities, United States companies | Level 2 | United States
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Pension | MEC | Equity securities, United States companies | Level 3 | United States
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	$ 0	$ 0
Pension | MEC | Investment funds | United States
Defined Benefit Plan Disclosure [Line Items]
Percentage of funds comprised of equity securities	56.00%	65.00%
Percentage of funds comprised of debt securities	44.00%	35.00%
Percentage of funds invested in United States securities	90.00%	82.00%
Percentage of funds invested in international securities	10.00%	18.00%
Pension | MEC | Investment funds | NAV | United States
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	$ 332	$ 393
Pension | MEC | Real estate funds | NAV | United States
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year		43
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 | MEC
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	308	278	$ 272
Other Postretirement | MEC | Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	308	278
Other Postretirement | MEC | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	271	203
Other Postretirement | MEC | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	37	75
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	8	11
Other Postretirement | MEC | Cash equivalents | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	8	11
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 | United States government obligations | Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	3	3
Other Postretirement | MEC | United States government obligations | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	3	3
Other Postretirement | MEC | United States government obligations | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	0	0
Other Postretirement | MEC | United States 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	6	7
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	6	7
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	28	65
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	28	65
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	3	3
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	3	3
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	82.00%	56.00%
Percentage of funds comprised of debt securities	18.00%	44.00%
Percentage of funds invested in United States securities	82.00%	56.00%
Percentage of funds invested in international securities	18.00%	44.00%
Other Postretirement | MEC | Investment funds | Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	$ 260	$ 189
Other Postretirement | MEC | Investment funds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value, end of year	260	189
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