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Derivatives and Financial Instruments - Narrative (Details)
$ in Millions
2 Months Ended 3 Months Ended 9 Months Ended
Aug. 31, 2019
USD ($)
Sep. 30, 2019
USD ($)
Sep. 30, 2018
USD ($)
Sep. 30, 2019
USD ($)
Sep. 30, 2018
USD ($)
Derivative [Line Items]          
Number of Interest Rate Derivatives Held   5   5  
Derivative, Term of Contract 2 years        
Investment income   $ 1 $ 1 $ 4 $ 4
Cash Flow Hedging | Designated as Hedging Instrument | Interest Rate Swap          
Derivative [Line Items]          
Notional amount $ 500