Employee Benefit Plans - Assumed Average Annual Rate of Increase in the Per Capita Cost of Covered Benefits (Details)	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Group Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Health care cost trend rate	7.00%	7.00%
Ultimate trend rate	5.00%	5.00%
Year rate reaches ultimate trend rate	2025	2025
Lifetime Prescription Cost
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Health care cost trend rate	9.00%	9.00%
Ultimate trend rate	5.00%	5.00%
Year rate reaches ultimate trend rate	2027	2027
Medicare Supplement
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Health care cost trend rate	4.50%	4.50%
Ultimate trend rate	4.50%	4.50%
Year rate reaches ultimate trend rate	2019	2018

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.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (l)
-URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920

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- Definition

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

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- Definition

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

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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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