Accumulated Other Comprehensive Income (Loss) Accumulated Other Comprehensive Income (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2020	Dec. 31, 2019
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Amounts reclassified from accumulated other comprehensive income (loss)	$ 20	$ (17)	$ 14	$ (52)
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Amounts reclassified from accumulated other comprehensive income (loss)	$ 20	$ (17)	$ 14	$ (51)