Share-based Compensation and Employee Benefits - Fair Value of Pension and OPEB Assets by Level of Assets (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Total plan assets fair value	$ 2,076	$ 1,864	$ 2,296
Pension Benefits | Fair Value, Inputs, Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Total plan assets fair value	763	743
Pension Benefits | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total plan assets fair value	296	308
Pension Benefits | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total plan assets fair value	467	435
Pension Benefits | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total plan assets fair value	0	0
Pension Benefits | Measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Total plan assets fair value	1,313	1,121
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	50	7
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	50	7
Pension Benefits | Short-term Investment Funds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total plan assets fair value	0	0
Pension Benefits | Mutual Funds | Fair Value, Inputs, Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Total plan assets fair value	0	81
Pension Benefits | Mutual Funds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total plan assets fair value	0	81
Pension Benefits | Mutual Funds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total plan assets fair value	0	0
Pension Benefits | Mutual Funds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total plan assets fair value	0	0
Pension Benefits | Equities | Fair Value, Inputs, Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Total plan assets fair value	296	227
Pension Benefits | Equities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total plan assets fair value	296	227
Pension Benefits | Equities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total plan assets fair value	0	0
Pension Benefits | Equities | Level 3
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	405	422
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	405	422
Pension Benefits | Fixed Income Securities | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total plan assets fair value	0	0
Pension Benefits | Derivatives | Fair Value, Inputs, Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Total plan assets fair value	12	6
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	12	6
Pension Benefits | Derivatives | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total plan assets fair value	0	0
Pension Benefits | Common/Collective Trusts | Measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Total plan assets fair value	$ 1,069	$ 857
Pension Benefits | Common/Collective Trusts Invested in Equity Securities | Measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Percentage of category allocated to investments	68.00%	63.00%
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	32.00%	37.00%
Pension Benefits | Private Investment Funds | Measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Total plan assets fair value	$ 200	$ 215
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	73.00%	71.00%
Pension Benefits | Private Investment Funds Invested in Equity Securities | Measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Percentage of category allocated to investments	27.00%	29.00%
Pension Benefits | Private Limited Partnerships | Measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Total plan assets fair value	$ 44	$ 49
OPEB
Defined Benefit Plan Disclosure [Line Items]
Total plan assets fair value	333	306	335
OPEB | Fair Value, Inputs, Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Total plan assets fair value	59	56
OPEB | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total plan assets fair value	37	1
OPEB | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total plan assets fair value	22	4
OPEB | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total plan assets fair value	0	51
OPEB | Measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Total plan assets fair value	274	250
OPEB | Cash | Fair Value, Inputs, Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Total plan assets fair value	1	0
OPEB | Cash | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total plan assets fair value	1	0
OPEB | Cash | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total plan assets fair value	0	0
OPEB | Cash | Level 3
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	4
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	4
OPEB | Short-term Investment Funds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total plan assets fair value	0	0
OPEB | Mutual Funds | Fair Value, Inputs, Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Total plan assets fair value	11	1
OPEB | Mutual Funds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total plan assets fair value	11	1
OPEB | Mutual Funds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total plan assets fair value	0	0
OPEB | Mutual Funds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total plan assets fair value	0	0
OPEB | Equities | Fair Value, Inputs, Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Total plan assets fair value	25	0
OPEB | Equities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total plan assets fair value	25	0
OPEB | Equities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total plan assets fair value	0	0
OPEB | Equities | Level 3
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	17	0
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	17	0
OPEB | Fixed Income Securities | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total plan assets fair value	0	0
OPEB | Guaranteed Insurance Contracts | Fair Value, Inputs, Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Total plan assets fair value	0	51
OPEB | Guaranteed Insurance Contracts | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total plan assets fair value	0	0
OPEB | Guaranteed Insurance Contracts | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total plan assets fair value	0	0
OPEB | Guaranteed Insurance Contracts | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total plan assets fair value	0	51	$ 49
OPEB | Common/Collective Trusts | Measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Total plan assets fair value	$ 274	$ 250
OPEB | Common/Collective Trusts Invested in Equity Securities | Measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Percentage of category allocated to investments	64.00%	60.00%
OPEB | Common/Collective Trusts Invested in Fixed Income Securities | Measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Percentage of category allocated to investments	36.00%	40.00%
Class P | Pension Benefits | Equities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Amount of KMI securities invested in	$ 129	$ 94
Class P | Pension Benefits | Fixed Income Securities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Amount of KMI securities invested in	$ 1