Debt (Bank Loans) (Details) - 12 months ended Mar. 31, 2017 $ in Millions, ₩ in Billions	USD ($)	KRW (₩)
BNDES Loans due February 2015 through April 2021 [Member]
Debt Instrument [Line Items]
Long-term debt, current	$ 2
Korea [Member] | Loans due November 2015 to September 2020 [Member]
Debt Instrument [Line Items]
Long-term debt, current	$ 93	₩ 103
Korea [Member] | Loans due November 2015 to September 2020 [Member] | Korea 91-day Certificate of Deposit Rate [Member] | Minimum [Member]
Debt Instrument [Line Items]
Basis spread on variable rate	0.91%
Korea [Member] | Loans due November 2015 to September 2020 [Member] | Korea 91-day Certificate of Deposit Rate [Member] | Maximum [Member]
Debt Instrument [Line Items]
Basis spread on variable rate	1.58%