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Share-Based Payments - Data Related to All Performance Share Awards (PSAs) (Details) - Performance Shares [Member]
shares in Millions, $ in Millions
12 Months Ended
Dec. 31, 2019
USD ($)
Dec. 31, 2018
USD ($)
Dec. 31, 2017
USD ($)
Employee
shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Total fair value of shares vested | $ $ 64 $ 4 $ 58
Total compensation cost related to nonvested awards not yet recognized, pre-tax | $ $ 34 $ 41 $ 34
Weighted-average period over which nonvested award cost is expected to be recognized (years) 1 year 9 months 18 days 1 year 9 months 18 days 1 year 9 months 18 days
Number of shares modified to accelerate vesting | shares     1.1
Number of employees affected by plan modification | Employee     90
Number of shares scheduled for near-term vesting | shares     1.1