| Income Taxes - Narrative (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended | ||
|---|---|---|---|---|
| Mar. 31, 2019 | Mar. 31, 2018 | Dec. 31, 2019 | Dec. 31, 2018 | |
| Investments, Owned, Federal Income Tax Note [Line Items] | ||||
| Income tax expense | $ 81 | $ 80 | ||
| Effective income tax rate percent | 33.30% | 21.70% | ||
| Valuation allowance | $ 88 | $ 66 | ||
| Forecast | ||||
| Investments, Owned, Federal Income Tax Note [Line Items] | ||||
| Effective income tax rate percent | 24.00% | |||
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- Definition Amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
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- Definition Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
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- Definition Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations. Reference 1: http://www.xbrl.org/2003/role/disclosureRef 
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. No definition available. 
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- Details 
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