Revenue from Contracts with Customers 4 (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Sep. 30, 2018	Sep. 30, 2018
Contract costs
Impairment loss on capitalized contract costs	$ 0	$ 0
Selling and Marketing
Contract costs
Amortization of capitalized contract costs	$ 31	$ 61
New Contracts
Contract costs
Capitalized contract costs, Amortization period		7 years
Renewal Contracts
Contract costs
Capitalized contract costs, Amortization period		3 years