Share-based Compensation and Employee Benefits - Schedule of Expected Payment of Future Benefits and Employer Contributions (Details) $ in Millions	Dec. 31, 2020 USD ($)
Pension Benefits
Expected Future Benefit Payments:
2021	$ 239
2022	238
2023	225
2024	219
2025	211
2026 - 2030	902
OPEB
Expected Future Benefit Payments:
2021	30
2022	28
2023	27
2024	25
2025	23
2026 - 2030	94
Expected Future Reductions Related to Medicare Prescription Drug, Improvement and Modernization Act of 2003:
2021	1
2022	1
2023	1
2024	1
2025	1
2026 - 2030	$ 6

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