Fair value measurements (Inflation and Discount Rate) (Details) - Significant Unobservable Inputs - Nonrecurring Fair Value Measurements	Mar. 31, 2020	Mar. 31, 2019
Inflation rate
Nonrecurring Fair Value Measurements
Asset retirement obligations, measurement input	0.0221	0.0225
Credit-adjusted risk-free discount rate
Nonrecurring Fair Value Measurements
Asset retirement obligations, measurement input	0.2500	0.1235

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.

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