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Fair Value Measurements - Narrative (Details) - USD ($)
$ in Millions
3 Months Ended
Jun. 30, 2019
Jun. 30, 2020
Dec. 31, 2019
South Africa Operations      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Impairment of assets held-for-sale $ 35    
Assets held-for-sale, fair value $ 5    
Level 2      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Long-term debt, fair value   $ 5,580 $ 5,000