Benefit Plans (Assumed long-term healthcare cost trend rate) (Details)	12 Months Ended
Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2013
Postemployment Benefits [Abstract]
Healthcare cost trend rate medical	7.00%	7.00%	8.00%
Healthcare prescription drug	7.00%ste_HealthcarePrescriptionDrug	7.00%ste_HealthcarePrescriptionDrug	7.00%ste_HealthcarePrescriptionDrug
Defined Benefit Plan, Ultimate Health Care Cost Trend Rate	4.50%	4.50%	4.50%

The assumed health care cost trend rate for the next year used to measure the expected cost of benefits covered by the plan (gross eligible charges). This is based upon the annual rate of change in the cost of health care benefits currently provided by the postretirement benefit plan, due to factors other than changes in the composition of the plan population by age and dependency status.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (l)

-URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Health Care Cost Trend Rate

-URI http://asc.fasb.org/extlink&oid=6514820

Name:	us-gaap_DefinedBenefitPlanHealthCareCostTrendRateAssumedForNextFiscalYear
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration