Cash Flows Reclassification - Restricted Cash ASU 2016-18 (Details) - Adjustments for New Accounting Pronouncement [Member] - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2016	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Restricted cash	$ 2,900	$ 2,500
Impact in restricted cash for operating activities	$ (358)

Amount of cash and cash equivalents restricted as to withdrawal or usage. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Name:	us-gaap_RestrictedCashAndCashEquivalents
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant