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Benefit Plans (Assumed long-term healthcare cost trend rate) (Details)
Mar. 31, 2019
Mar. 31, 2018
Mar. 31, 2017
Postemployment Benefits [Abstract]      
Healthcare cost trend rate medical 6.80% 7.00% 7.00%
Healthcare prescription drug 6.80% 7.00% 7.00%
Defined Benefit Plan, Ultimate Health Care Cost Trend Rate 4.50% 4.50% 4.50%