Income Taxes (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Income Tax Footnote Disclosure [Line Items]
Effective tax rates	5.00%	3.50%	59.40%	13.90%
United States statutory tax rate	35.00%	35.00%	35.00%	35.00%
Unrecognized tax benefits, period increase (decrease)	$ 9		$ 7
Gross unrecognized tax benefits	304		304
Cash deposits to offset uncertain tax liabilities	46		46
Amount of unrecognized tax benefits that would affect the effective tax rate	110		110
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	181		181
Unrecognized tax benefits income tax penalties and interest accrued increase (decrease)	1		2
Combined amount of accrued interest and penalties related to uncertain tax positions	25		25
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	$ 82		$ 82