Income Taxes (Schedule of Unrecognized Tax Benefits and Consolidated Liability for Tax Contingencies) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Unrecognized tax benefits	$ 66	$ 169	$ 158	$ 258
Accrued interest and penalties	9	23
Tax credits and other indirect benefits	(1)	(6)
Liability for tax contingencies	$ 74	$ 186

Amount accrued for interest on an underpayment of income taxes and penalties related to a tax position claimed or expected to be claimed in the tax return.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32718-109319

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Data Type:	xbrli:monetaryItemType
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