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Fair Value Disclosures - Narrative (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
carrying value $ 12,903 $ 12,224
Level 2    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Estimated fair value of long-term debt portfolio 13,611 $ 12,375
Level 3    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Beginning balance 28  
Foreign currency movement 3  
Gains recognized in interest expense - net 16  
Ending balance $ 47