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Share-based Compensation and Employee Benefits - Fair Value of Pension and OPEB Assets by Level of Assets (Details) - USD ($) $ in Millions | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
--- | --- | --- | ---
Pension Benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total plan assets fair value | $ 2,199 | $ 2,076 | $ 1,864
Pension Benefits | Fair Value, Inputs, Level 1, 2 and 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total plan assets fair value | 762 | 763 |
Pension Benefits | Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total plan assets fair value | 249 | 296 |
Pension Benefits | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total plan assets fair value | 513 | 467 |
Pension Benefits | Measured at NAV |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total plan assets fair value | 1,437 | 1,313 |
Pension Benefits | Short-term Investment Funds | Fair Value, Inputs, Level 1, 2 and 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total plan assets fair value | 77 | 50 |
Pension Benefits | Short-term Investment Funds | Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total plan assets fair value | 0 | 0 |
Pension Benefits | Short-term Investment Funds | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total plan assets fair value | 77 | 50 |
Pension Benefits | Equities | Fair Value, Inputs, Level 1, 2 and 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total plan assets fair value | 249 | 296 |
Pension Benefits | Equities | Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total plan assets fair value | 249 | 296 |
Pension Benefits | Equities | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total plan assets fair value | 0 | 0 |
Pension Benefits | Fixed Income Securities | Fair Value, Inputs, Level 1, 2 and 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total plan assets fair value | 425 | 405 |
Pension Benefits | Fixed Income Securities | Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total plan assets fair value | 0 | 0 |
Pension Benefits | Fixed Income Securities | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total plan assets fair value | 425 | 405 |
Amount of KMI securities invested in | 1 | 1 |
Pension Benefits | Derivatives | Fair Value, Inputs, Level 1, 2 and 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total plan assets fair value | 11 | 12 |
Pension Benefits | Derivatives | Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total plan assets fair value | 0 | 0 |
Pension Benefits | Derivatives | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total plan assets fair value | 11 | 12 |
Pension Benefits | Common/Collective Trusts | Measured at NAV |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total plan assets fair value | $ 1,184 | $ 1,069 |
Pension Benefits | Common/Collective Trusts Invested in Equity Securities | Measured at NAV |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Percentage of category allocated to investments | 71.00% | 68.00% |
Pension Benefits | Common/Collective Trusts Invested in Fixed Income Securities | Measured at NAV |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Percentage of category allocated to investments | 29.00% | 32.00% |
Pension Benefits | Private Investment Funds | Measured at NAV |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total plan assets fair value | $ 208 | $ 200 |
Pension Benefits | Private Investment Funds Invested in Fixed Income Securities | Measured at NAV |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Percentage of category allocated to investments | 71.00% | 73.00% |
Pension Benefits | Private Investment Funds Invested in Equity Securities | Measured at NAV |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Percentage of category allocated to investments | 29.00% | 27.00% |
Pension Benefits | Private Limited Partnerships | Measured at NAV |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total plan assets fair value | $ 45 | $ 44 |
OPEB |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total plan assets fair value | 361 | 333 | $ 306
OPEB | Fair Value, Inputs, Level 1, 2 and 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total plan assets fair value | 5 | 59 |
OPEB | Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total plan assets fair value | 0 | 37 |
OPEB | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total plan assets fair value | 5 | 22 |
OPEB | Measured at NAV |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total plan assets fair value | 356 | 274 |
OPEB | Cash | Fair Value, Inputs, Level 1, 2 and 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total plan assets fair value | 0 | 1 |
OPEB | Cash | Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total plan assets fair value | 0 | 1 |
OPEB | Cash | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total plan assets fair value | 0 | 0 |
OPEB | Short-term Investment Funds | Fair Value, Inputs, Level 1, 2 and 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total plan assets fair value | 5 | 5 |
OPEB | Short-term Investment Funds | Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total plan assets fair value | 0 | 0 |
OPEB | Short-term Investment Funds | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total plan assets fair value | 5 | 5 |
OPEB | Equities | Fair Value, Inputs, Level 1, 2 and 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total plan assets fair value | 0 | 25 |
OPEB | Equities | Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total plan assets fair value | 0 | 25 |
OPEB | Equities | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total plan assets fair value | 0 | 0 |
OPEB | Fixed Income Securities | Fair Value, Inputs, Level 1, 2 and 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total plan assets fair value | 0 | 17 |
OPEB | Fixed Income Securities | Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total plan assets fair value | 0 | 0 |
OPEB | Fixed Income Securities | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total plan assets fair value | 0 | 17 |
OPEB | Mutual Funds | Fair Value, Inputs, Level 1, 2 and 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total plan assets fair value | 0 | 11 |
OPEB | Mutual Funds | Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total plan assets fair value | 0 | 11 |
OPEB | Mutual Funds | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total plan assets fair value | 0 | 0 |
OPEB | Common/Collective Trusts | Measured at NAV |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total plan assets fair value | $ 356 | $ 274 |
OPEB | Common/Collective Trusts Invested in Equity Securities | Measured at NAV |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Percentage of category allocated to investments | 65.00% | 64.00% |
OPEB | Common/Collective Trusts Invested in Fixed Income Securities | Measured at NAV |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Percentage of category allocated to investments | 35.00% | 36.00% |
Class P | Pension Benefits | Equities | Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Amount of KMI securities invested in | $ 83 | $ 129 |

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