Employee Benefit Plans (Schedule of Health Care Costs Trend Rates) (Details)	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Medicare Eligible Claims [Member]
Defined Benefit Plan, Assumed Health Care Cost Trend Rates [Abstract]
Defined Benefit Plan, Health Care Cost Trend Rate Assumed, Next Fiscal Year	10.00%	8.00%
Defined Benefit Plan, Assumed Health Care Cost Trend Rate, Description	9% down to 5% in 2024	10% down to 5% in 2024
Defined Benefit Plan, Year Health Care Cost Trend Rate Reaches Ultimate Trend Rate	2024	2020
Defined Benefit Plan, Ultimate Health Care Cost Trend Rate	5.00%	5.00%
Pre Medicare Eligible Claims [Member]
Defined Benefit Plan, Assumed Health Care Cost Trend Rates [Abstract]
Defined Benefit Plan, Health Care Cost Trend Rate Assumed, Next Fiscal Year	10.00%	8.00%
Defined Benefit Plan, Assumed Health Care Cost Trend Rate, Description	9% down to 5% in 2024	10% down to 5% in 2024
Defined Benefit Plan, Year Health Care Cost Trend Rate Reaches Ultimate Trend Rate	2024	2020
Defined Benefit Plan, Ultimate Health Care Cost Trend Rate	5.00%	5.00%

No definition available.

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- Definition

Description of direction and pattern of change in assumed health care cost trend rate used to measure expected cost of benefits for defined benefit postretirement plan.

+ References

No definition available.

+ Details

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- Definition

Assumed rate, for next fiscal year, based on annual change in cost of health care cost benefits used to measure expected cost of benefits covered by defined benefit postretirement plan. Factors include, but are not limited to, estimate of health care inflation, change in health care utilization or delivery pattern, technological advances, and change in health status of participant. Excludes factors for change in composition of plan population by age and dependency status.

+ 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 (l)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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- Definition

Ultimate trend rate for health care cost for defined benefit postretirement plan.

+ References

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- Definition

Year ultimate health care cost trend rate is expected to be reached, in CCYY format.

+ References

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