Hedging Activities - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Mar. 31, 2015
Minimum
Derivative [Line Items]
Derivative, maturity date			Mar. 31, 2016
Maximum
Derivative [Line Items]
Derivative, maturity date			Mar. 31, 2020
Foreign Exchange Contract
Derivative [Line Items]
Description of foreign currency derivative activities			manage the impact of foreign currency fluctuations
Foreign Exchange Contract | Derivatives designated for hedge accounting
Derivative [Line Items]
Notional values designated for hedge accounting	$ 399		$ 399		$ 399
Foreign Exchange Contract | Derivatives not designated for hedge accounting
Derivative [Line Items]
Notional values designated for hedge accounting	1,894		1,894		$ 1,755
Net gains (losses) from changes in fair value not designated for hedge accounting	$ 67	$ (30)	$ 22	$ (50)
Foreign Exchange Contract | Derivatives not designated for hedge accounting | Minimum
Derivative [Line Items]
Maturity of foreign currency derivatives			Oct. 31, 2015
Foreign Exchange Contract | Derivatives not designated for hedge accounting | Maximum
Derivative [Line Items]
Maturity of foreign currency derivatives			Jun. 15, 2016