Accumulated Other Comprehensive Income (Loss) Accumulated Other Comprehensive Income (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Amounts reclassified from accumulated other comprehensive income (loss)	$ 14	$ (1)	$ 25	$ (6)
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)	$ 14	$ (1)	$ 25	$ (6)