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Acquisitions, Discontinued Operations and Dispositions - Acquisitions (Details) customer in Thousands, $ in Millions |  | 12 Months Ended |
--- | --- | --- | ---
Jun. 01, 2018 USD ($) state customer | Dec. 31, 2018 USD ($) customer | Dec. 31, 2017 USD ($)
Business Acquisition [Line Items] |  |  |
Goodwill |  | $ 573 | $ 539
XOOM Energy, LLC |  |  |
Business Acquisition [Line Items] |  |  |
Number of states in which the entity operates | state | 19 |  |
Consideration transferred | $ 213 |  |
Customers acquired | customer | 300 |  |
Net current and non-current working capital | $ 46 |  |
Other intangible assets | 133 |  |
Goodwill | $ 34 |  |
Small Book Acquisitions |  |  |
Business Acquisition [Line Items] |  |  |
Consideration transferred |  | $ 44 |
Customers acquired | customer |  | 115 |

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