Income Taxes - Uncertain Tax Positions (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Beginning of year	$ 28	$ 50	$ 40
Effect of provision to tax return filing adjustments	1	8	6
Increase in unrecognized tax positions as a result of position taken during the current period	0	1	4
Decrease in unrecognized tax positions as a result of settlement of positions taken during the prior period	0	(31)	0
Balance as of December 31,	14	28	50
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations	$ (15)	$ 0	$ 0

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

No definition available.

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- Definition

Amount of unrecognized tax benefits.

+ References

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Amount of decrease in unrecognized tax benefits resulting from settlements with taxing authorities.

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Amount of increase in unrecognized tax benefits resulting from tax positions that have been or will be taken in current period tax return.

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Amount of increase in unrecognized tax benefits resulting from tax positions taken in prior period tax returns.

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Amount of decrease in unrecognized tax benefits resulting from lapses of applicable statutes of limitations.

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