Financial Instruments (Narrative) (Details) - USD ($) $ in Millions	9 Months Ended
	Dec. 31, 2016	May 31, 2016	Mar. 31, 2016	Dec. 31, 2015
Sale Leaseback Transaction [Line Items]
Sale Leaseback Transaction, Net Book Value	$ 447		$ 1,200	$ 1,300
Repayments of Accounts Receivable Securitization	502
Short-term Investments	$ 2,349		0
Document Period End Date	Dec. 31, 2016
Marketable Securities, Equity Securities	$ 50		$ 46
MLS 2nd Tranche [Member]
Sale Leaseback Transaction [Line Items]
Sale Leaseback Transaction, Net Book Value	554	$ 1,300
Sale Leaseback Transaction, Current Period Gain Recognized	$ 30