Income Taxes (Uncertain Tax Positions Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Jan. 31, 2018	Dec. 31, 2017
Income Tax Examination [Line Items]
Income Tax Examination, pre-tax adjustments proposed		$ 198	$ 192
Income Tax Examination, Estimate of Possible Loss	$ 136

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

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