Income Taxes (Reconciliation 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]
Gross unrecognized tax benefits, January 1	$ 1,497	$ 1,443	$ 1,441
Additions based on tax positions related to the current year	229	121	74
Additions based on tax positions related to prior years	125	319	72
Additions from acquired subsidiaries	130	0	13
Reductions for tax positions of prior years	(346)	(251)	(66)
Reductions due to expiration of statutes of limitations	(75)	(70)	(44)
Settlements with tax authorities	(17)	(65)	(47)
Gross unrecognized tax benefits, December 31	1,543	1,497	1,443
Positions paid	(531)	(688)	(340)
Liability for uncertain tax positions	$ 1,012	$ 809	$ 1,103

Unrecognized Tax Benefits Increases Resulting From Acquired Subsidiaries

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Unrecognized tax benefits associated with positions for which tax has been assessed and paid.

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Amount recognized for uncertainty in income taxes classified as noncurrent.

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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.

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Amount of unrecognized tax benefits.

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

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