Income Taxes (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Mar. 31, 2017
Income Tax Disclosure [Abstract]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent			35.00%
Income Tax Reconciliation, Change in Deferred Tax Assets Valuation Allowance			$ 60	$ 314
Income tax benefit	$ 98	$ 119	390	175
Tax benefit from organizational restructuring			0	(42)
Increase deferred tax liability for business activity changes			65	0
Unrecognized tax benefit	$ 207		207		$ 190
Income Taxes Paid, Net			$ 52	$ 31