Income Taxes (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2015	Dec. 31, 2014
Income Tax Footnote Disclosure [Line Items]
Deferred Tax Assets, Valuation Allowance	$ 539		$ 539
Effective tax rates	50.00%	9.00%	26.80%	9.10%
United States statutory tax rate	35.00%		35.00%
Excess Tax Benefit from Share-based Compensation, Financing Activities	$ 8		$ 73	$ 16
Unrecognized tax benefits, period increase (decrease)	40		57
Gross unrecognized tax benefits	311		311
Amount of unrecognized tax benefits that would affect the effective tax rate	51		51
The total amount of unrecognized tax benefits that, if recognized, would result in adjustments to deferred tax assets with corresponding adjustments to the valuation allowance			260
Income Tax Examination, Penalties and Interest Accrued	2		2
Combined amount of accrued interest and penalties related to uncertain tax positions	14		14
Maximum
Income Tax Footnote Disclosure [Line Items]
Amount of unrecognized tax benefits for which it is reasonably possible that there will be a reduction within the next 12 months	$ 50		$ 50