Income Tax (Interest Accrued Related to Unrecognized Tax Benefits) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Interest recognized on the consolidated statements of operations (1)	$ 37	$ (41)	$ 388
Interest included in other liabilities on the consolidated balance sheets	$ 659	$ 623

Amount of interest expense accrued for an underpayment of income taxes.

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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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant