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Goodwill and Other Intangible Assets - Other Intangible Assets (Detail)
$ in Millions
12 Months Ended
Dec. 31, 2017
USD ($)
Finite-Lived Intangible Assets [Line Items]  
Expected aggregate amortization expense for intangible assets in 2018 $ 31
Expected aggregate amortization expense for intangible assets in 2019 31
Expected aggregate amortization expense for intangible assets in 2020 31
Expected aggregate amortization expense for intangible assets in 2021 31
Expected aggregate amortization expense for intangible assets in 2022 $ 31
Customer Contracts [Member] | Gathering and Processing Assets in the Delaware basin [Member]  
Finite-Lived Intangible Assets [Line Items]  
Acquired intangible assets, useful life 30 years