Intangible Assets (Narrative) (Details) - USD ($) $ in Millions	6 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Document Period End Date	Sep. 30, 2017
Other, Net [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Gain (Loss) on Disposition of Intangible Assets	$ 479	$ 354