Income Taxes - Summary of 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]
Balance at beginning of year	$ 283	$ 174	$ 315
Additions for tax positions related to prior years	37	3	77
Additions for tax positions related to the current year	16	126	9
Reductions for tax positions related to prior years	(15)	(10)	(204)
Settlements	0	(9)	(21)
Lapse of statute of limitations	(3)	(2)	(2)
Currency translation adjustment	0	1	0
Balance at end of year	$ 318	$ 283	$ 174

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 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 foreign currency translation.

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

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