Income Taxes (Changes in Liability for Unrecognized Tax Benefits) (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 balance of gross unrecognized tax benefits	$ 18	$ 22	$ 26
Increases: Positions taken during a prior period	212	4	14
Decreases: Positions taken during a prior period	(16)	(3)	(14)
Decreases: Settlements with taxing authorities	(7)	(4)
Decreases: Reductions resulting from lapse of statute of limitations		(1)	(4)
Ending balance of gross unrecognized tax benefits	207	18	22
Favorable (unfavorable) impact if recognized	$ 76	$ 17	$ 18

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.

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Amount of decrease 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 settlements with taxing authorities.

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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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The total amount of unrecognized tax benefits that, if recognized, would affect the effective tax rate.

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