Accounting Policies (Details) - USD ($) $ in Millions	6 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Mar. 31, 2017
Accounting Policies [Abstract]
Percentage of cash and cash equivalents held by the Company's foreign subsidiaries outside the United States	66.00%
Accounting Policies [Line Items]
Payments related to tax withholding for share-based compensation	$ 35	$ 34
Minimum
Accounting Policies [Line Items]
Capitalized contract costs, Amortization period	4 years
Maximum
Accounting Policies [Line Items]
Capitalized contract costs, Amortization period	7 years
Reclass from Operating Activities to Financing Activities
Accounting Policies [Line Items]
Payments related to tax withholding for share-based compensation		$ 34
Other Noncurrent Assets, Net
Accounting Policies [Line Items]
Restricted cash	$ 2		$ 1