Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Income Tax Disclosure [Abstract]
Income tax expense	$ 74	$ 94	$ 134	$ 173
Net discrete tax benefit			$ 8
Estimated annual effective tax rate, which excludes impact of discrete items			28.60%	29.00%
Minimum
Expected Effective Tax Rate [Line Items]
Expected fiscal year 2018 effective tax rate			28.00%
Maximum
Expected Effective Tax Rate [Line Items]
Expected fiscal year 2018 effective tax rate			29.00%