Quarterly report pursuant to Section 13 or 15(d)

Borrowings (Credit Facility) (Narrative) (Details)

v3.8.0.1
Borrowings (Credit Facility) (Narrative) (Details)
9 Months Ended
Sep. 30, 2017
USD ($)
May 31, 2017
USD ($)
lender
Dec. 31, 2016
USD ($)
Line of Credit Facility [Line Items]      
Balance outstanding on credit facility $ 0   $ 0
Senior secured revolving credit facility      
Line of Credit Facility [Line Items]      
Debt instrument maturity date May 25, 2022    
Institutional lenders | lender   17  
Maximum borrowing capacity   $ 2,000,000,000  
Increase limit $ 650,000,000    
Credit facility borrowing base 500,000,000    
Balance outstanding on credit facility $ 0    
Interest rate at period end (as a percent) 3.23%    
Unused capacity, commitment fee (as a percent) 0.375%    
Senior secured revolving credit facility | Minimum      
Line of Credit Facility [Line Items]      
Debt instrument interest rate (as a percent) 2.00%    
Senior secured revolving credit facility | Maximum      
Line of Credit Facility [Line Items]      
Debt instrument interest rate (as a percent) 3.00%