Debt (Other Long-term Debt) (Details) SFr in Millions, $ in Millions	1 Months Ended		12 Months Ended
	Dec. 31, 2004 USD ($)	Dec. 31, 2004 CHF (SFr)	Mar. 31, 2017 USD ($)	Mar. 31, 2016
Debt Instrument [Line Items]
Capital leases, term of contract			15 years
Quarterly capital lease payments | SFr		SFr 1.7
Principal obligation on capital leases			$ 19.0
Information Technology [Member]
Debt Instrument [Line Items]
Capital leases, term of contract				5 years
Other Capital Leases [Member]
Debt Instrument [Line Items]
Principal obligation on capital leases			$ 1.0
Alcan [Member]
Debt Instrument [Line Items]
Capital leases, term of contract	15 years	15 years
Interest rate	7.50%	7.50%
Quarterly capital lease payments	$ 1.7