Income Taxes - Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits at beginning of year	$ 394	$ 221	$ 179
Gross increases - current year tax positions	1,566	57	52
Gross increases - prior year tax positions	16	128	44
Gross decreases - prior year tax positions	(36)	(12)	(54)
Gross decreases - settlements with tax authorities	(143)	0	0
Unrecognized tax benefits at end of year	$ 1,797	$ 394	$ 221

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 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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