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Acquisitions and Dispositions - Amortization Expense (Details) - ACC Acquisition
$ in Millions
8 Months Ended
Feb. 14, 2017
contract
Sep. 30, 2017
USD ($)
Business Acquisition [Line Items]    
Finite lived intangible assets, useful life 20 years  
Acreage dedication contracts    
Business Acquisition [Line Items]    
Number of acreage dedication contracts | contract 5  
Finite lived intangible assets, useful life 20 years  
Amortization of finite lived intangible assets   $ 7
Remainder of 2017   3
2018   25
2019   34
2020   42
2021   $ 48