Share-based Compensation and Employee Benefits - Schedule of Expected Payment of Future Benefits and Employer Contributions (Details) $ in Millions	Dec. 31, 2019 USD ($)
Pension Benefits
Expected Future Benefit Payments:
2020	$ 239
2021	230
2022	229
2023	218
2024	212
2025 - 2029	939
OPEB
Expected Future Benefit Payments:
2020	32
2021	31
2022	30
2023	29
2024	27
2025 - 2029	115
Expected Future Reductions Related to Medicare Prescription Drug, Improvement and Modernization Act of 2003:
2020	1
2021	1
2022	1
2023	1
2024	1
2025 - 2029	$ 6

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