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Commitments and Contingencies (Unconditional Purchase Obligations - Narrative) (Details)
$ in Billions
Jun. 30, 2020
USD ($)
Unrecorded Unconditional Purchase Obligation [Line Items]  
Unconditional purchase obligation $ 10.2
Helium Purchases  
Unrecorded Unconditional Purchase Obligation [Line Items]  
Unconditional purchase obligation $ 8.6