Stockholders' Equity - Other Comprehensive Income (Loss), Net of Tax (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Foreign currency translation adjustments
Foreign currency translation adjustments arising during period, net of income tax expense of nil, nil, nil and nil	$ (243)	$ (667)	$ 104	$ (569)
Reclassified to income statement, net of income tax expense of nil, nil, nil and nil	0	(10)	0	(10)
Foreign currency translation adjustments	(243)	(677)	104	(579)
Unrealized gains (losses) on cash flow hedges
Unrealized gains (losses) on cash flow hedges arising during period, net of income tax expense of nil, nil, nil and nil	2	0	6	(2)
Changes in retirement-related benefit plans
Net actuarial gain (loss) and prior service cost arising during the period, net of income tax benefit of $1, nil, $9 and nil	1	0	(28)	0
Amortization of actuarial loss and prior service costs, net of income tax expense of $5, $2, $9 and $3	8	3	15	6
Foreign currency translation adjustments, net of income tax expense of nil, nil, nil and nil	2	3	(4)	2
Changes in retirement-related benefit plans	11	6	(17)	8
Other comprehensive income (loss), net of tax	(230)	(671)	93	(573)
Foreign currency translation adjustments arising during period, income tax expense	0	0	0	0
Reclassified to income statement, income tax expense	0	0	0	0
Unrealized gains (losses) on cash flow hedges arising during period, income tax expense	0	0	0	0
Net actuarial gain (loss) and prior service cost arising during the period, income tax benefit	1	0	9	0
Amortization of actuarial loss and prior service costs, income tax expense	5	2	9	3
Foreign currency translation adjustments, income tax expense	$ 0	$ 0	$ 0	$ 0