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Income Tax (Narrative) (Detail) - USD ($) $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | Sep. 01, 2016
Income Taxes [Line Items] |  |  |  |
Provision/(benefit) for income taxes | $ 8 | $ 1 | $ (12) |
Income tax rate | 1.00% | 1.00% | 5.00% |
Deferred tax liabilities, net | $ 13 | $ 5 |  |
Net penalties and interest expense (benefits) | (1) |  | $ 1 |
Penalties and interest accrued | $ 0 | $ 0 | $ 0 |
Federal | Minimum |  |  |  |
Income Taxes [Line Items] |  |  |  |
Open tax year | 2015 |  |  |
Federal | Maximum |  |  |  |
Income Taxes [Line Items] |  |  |  |
Open tax year | 2016 |  |  |
State | Minimum |  |  |  |
Income Taxes [Line Items] |  |  |  |
Open tax year | 2013 |  |  |
State | Maximum |  |  |  |
Income Taxes [Line Items] |  |  |  |
Open tax year | 2017 |  |  |
MPC |  |  |  |
Income Taxes [Line Items] |  |  |  |
Deferred tax liabilities assumed |  |  |  | $ 377

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