Income Taxes (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2019	Jan. 31, 2018
Tax Credit Carryforward [Line Items]
Income Tax Examination, pre-tax adjustments proposed		$ 198
Income Tax Examination, Estimate of Possible Loss	$ 69

Estimated amount of loss resulting from an adverse tax position.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (d)(3)
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32718-109319

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration