Estimated net loss and prior service credit (Details 4) - Qualified Plan	Dec. 31, 2020 USD ($)
Underfunded Plan \| Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Expected Amortization of Gain (Loss), Next Fiscal Year	$ (8,000,000.0)
Overfunded Plan \| Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Expected Amortization of Gain (Loss), Next Fiscal Year	(24,000)
Defined benefit plan, amortization of net prior service cost (credit)	$ (1,400,000)

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.

No definition available.

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+ References

Reference 1: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (s)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920

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Amount included in accumulated other comprehensive (income) loss for prior service cost (credit) expected to be recognized in net periodic benefit cost (credit) for fiscal year following most recent annual statement of financial position.

+ References

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