Significant Accounting Policies (Narrative) (Details) $ in Millions	6 Months Ended
Jun. 30, 2017 USD ($)
Significant Accounting Policies [Abstract]
Cumulative tax benefits in beginning retained earnings	$ 233

Amount of cumulative tax effect on beginning retained earnings from change in accounting principle.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 20
-Section 45
-Paragraph 11
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=65896914&loc=d3e39076-109324

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