Income Taxes - Reconciliation of Tax Contingencies (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]
Gross tax contingencies – beginning of period	$ 3,414	$ 2,309	$ 1,710
Gross increases to tax positions in prior periods	216	164	223
Gross decreases to tax positions in prior periods	(181)	(90)	(139)
Gross increases to current period tax positions	707	1,088	518
Settlements with tax authorities	(207)	(36)	0
Lapse of statute of limitations	(26)	(21)	(3)
Gross tax contingencies - end of period	3,923	$ 3,414	$ 2,309
Tax contingencies, that if fully recognized, would decrease our effective tax rate	$ 2,100

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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Amount of unrecognized tax benefits.

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