Stock-Based Compensation - Restricted Stocks, Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Employee Stock Ownership Plan (ESOP) Disclosures
Stock-based compensation expense	$ 123	$ 132	$ 127
Restricted Stock Awards
Employee Stock Ownership Plan (ESOP) Disclosures
Total grant-date fair value	0	16	27
Restricted Stock Units
Employee Stock Ownership Plan (ESOP) Disclosures
Total grant-date fair value	107	$ 73	$ 42
Stock-based compensation expense	$ 119
Weighted-average period over which expense is expected to be recognized	2 years 4 months 24 days

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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