Taxes - Unrecognized Tax Benefits Reconciliation (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Taxes
Increase (decrease) in amount of unrecognized tax benefits	$ (272)
Reconciliation of the beginning and ending amount of unrecognized tax benefits
Balance at January 1	7,031	$ 3,740	$ 4,574
Additions based on tax positions related to the current year	394	3,029	560
Additions for tax positions of prior years	1,201	803	334
Reductions for tax positions of prior years (including impacts due to a lapse of statute)	(1,686)	(367)	(1,443)
Settlements	(181)	(174)	(285)
Balance at December 31	$ 6,759	$ 7,031	$ 3,740

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

+ References

No definition available.

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Amount of unrecognized tax benefits.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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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 tax positions taken in prior period tax returns.

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Amount of increase (decrease) in unrecognized tax benefits attributable to uncertain tax positions taken in tax returns.

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