Investments - Schedule of maturities for short-term investments (Details) $ in Millions	Mar. 31, 2017 USD ($)
Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity
Due in one year or less	$ 216
Due after one year through three years	434
Due after three years through five years	72
Due after five years	21
Total	$ 743