Accumulated Other Comprehensive Income Accumulated Other Comprehensive Income (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2015	Dec. 31, 2014
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	$ 3	$ 0	$ 11	$ (7)
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	$ 4	$ (1)	$ 11	$ (8)