Stock-Based Compensation (Schedule of Stock Options) (Details) - Stock Options $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Mar. 31, 2017 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding at the beginning of period (in shares)	0
Assumed (in shares)	24
Exercised (in shares)	(4)
Outstanding at the end of period (in shares)	20
Exercisable at period end (in shares)	7
Vested and expected to vest at period end (in shares)	18
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Weighted Average Exercise Price, Outstanding at the beginning of period (in dollars per share) | $ / shares	$ 0.00
Weighted Average Exercise Price, Assumed (in dollars per share) | $ / shares	8.77
Weighted Average Exercise Price, Exercised (in dollars per share) | $ / shares	7.93
Weighted Average Exercise Price, Outstanding at the end of period (in dollars per share) | $ / shares	$ 8.94
Exercisable at period end, Weighted Average Remaining Years (in years)	8 years 3 months 12 days
Exercisable at period end, Aggregate Intrinsic Value | $	$ 164
Vested and expected to vest at period end, Weighted Average Remaining Years (in years)	8 years 4 months 12 days
Vested and expected to vest at period end, Aggregate Intrinsic Value | $	$ 392
Intrinsic value of options exercised | $	78
Total unrecognized compensation cost adjusted for estimated forfeitures | $	$ 147
Weighted-average period in years over which stock based compensation cost is expected to be recognized (in years)	1 year 8 months