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Basis of Presentation - Adoption of New Accounting Standards - Narrative (Details) - USD ($)
$ in Millions
Mar. 31, 2019
Jan. 01, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]    
Additional Assets $ 1,096  
Accounting Standards Update 2016-02    
New Accounting Pronouncements or Change in Accounting Principle [Line Items]    
Additional Assets   $ 1,100