Income Taxes, Reconciliation Between the U.S. Federal Statutory Rate and the Effective Tax Rate (Details)	9 Months Ended	12 Months Ended
	Dec. 31, 2017	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Reconciliation of federal statutory income tax rate to company's effective income tax rate [Abstract]
Statutory federal tax	35.00%	31.50%	35.00%	35.00%
State taxes, net of federal benefit		2.90%	(3.30%)	11.50%
Taxes on non-U.S. earnings and losses		(3.80%)	(3.50%)	26.40%
Valuation allowance		(5.60%)	1.20%	(20.90%)
Tax credits		(17.30%)	(9.00%)	20.50%
Compensation		(0.80%)	2.90%	(3.70%)
Tax rate or law changes		60.10%	(2.50%)	1.30%
Uncertain tax positions, net of settlements		(0.80%)	5.60%	(4.30%)
Notional interest deductions		(3.20%)	(8.80%)	0.00%
Dividend repatriation		0.20%	7.10%	16.00%
Other		(0.80%)	3.70%	8.10%
Effective tax rate		62.40%	28.40%	89.90%