Pension and Other Post-Employment Benefits (Real Estate And Other Investments) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets, Beginning of Year	$ 194
Fair Value of Plan Assets, End of Year	210	$ 194
Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets, Beginning of Year	10
Fair Value of Plan Assets, End of Year	11	10
Real Estate And Other [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets, Beginning of Year	10
Fair Value of Plan Assets, End of Year	11	10
Real Estate And Other [Member] \| Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets, Beginning of Year	10	10
Return On Plan Assets Relating to Assets Still Held at the reporting date	1	0
Fair Value of Plan Assets, End of Year	$ 11	$ 10

Amount, measured using unobservable inputs, of increase (decrease) in plan assets of defined benefit plan from actual return (loss) on assets still held.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(5)(iv)(02)(A)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

Fair value of assets that have been segregated and restricted to provide pension or postretirement benefits. Assets include, but are not limited to, stocks, bonds, other investments, earnings from investments, and contributions by the employer and employees.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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