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Leases - Components of Lease Expense (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Leases [Abstract]      
Operating lease expense $ 28 $ 34  
Finance lease expense:      
Amortization of ROU assets 19 17 $ 0
Interest on lease liabilities 15 15  
Total finance lease expense $ 34 $ 32