Quarterly report pursuant to Section 13 or 15(d)

Other Non-Current Assets - Equity Method Investments (Details)

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Other Non-Current Assets - Equity Method Investments (Details)
3 Months Ended 6 Months Ended
Jun. 30, 2018
USD ($)
Jun. 30, 2017
USD ($)
Jun. 30, 2018
USD ($)
mi
Jun. 30, 2017
USD ($)
Dec. 31, 2017
USD ($)
Investment [Line Items]          
Equity method investment $ 64,000,000   $ 64,000,000   $ 64,000,000
Other—related party 3,000,000 $ 1,000,000 4,000,000 $ 1,000,000  
Accounts receivable—related party 2,000,000   2,000,000   2,000,000
Midship Holdings [Member]          
Investment [Line Items]          
Equity method investment 55,000,000   55,000,000   55,000,000
O&M Services [Member] | Midship Pipeline [Member] | Service Agreements [Member]          
Investment [Line Items]          
Other—related party 3,000,000 $ 1,000,000 4,000,000 $ 1,000,000  
Accounts receivable—related party 2,000,000   $ 2,000,000   $ 2,000,000
CCL [Member] | Midship Pipeline [Member] | Natural Gas Transportation Agreement [Member]          
Investment [Line Items]          
Long-term Purchase Commitment, Period     10 years    
EIG [Member] | Maximum [Member]          
Investment [Line Items]          
Investment Company, Financial Commitment to Investee, Future Amount 500,000,000   $ 500,000,000    
Midship Pipeline [Member]          
Investment [Line Items]          
Length Of Natural Gas Pipeline | mi     200    
Midship Pipeline [Member] | CCL [Member] | Midship Pipeline Letter of Credit [Member]          
Investment [Line Items]          
Letter of Credit, Maximum Borrowing Capacity 16,000,000   $ 16,000,000    
Letters of credit issued $ 0   $ 0