Income Taxes (Tables)

6 Months Ended

Sep. 30, 2018

Income Tax Disclosure [Abstract]

Factors Causing Variation in Effective Tax Rate From US Federal Statutory Rate

The differences that caused our effective income tax rates to differ from the U.S. federal statutory rates for the six-month periods endedSeptember 30, 2018 and 2017, respectively, were as follows:

	Six Months Ended September 30,
	2018			2017
	(in millions)
Income tax expense at the federal statutory rate	$	(93	)	$	(192	)
Effect of:
State income taxes, net of federal income tax effect	(34		)	(38		)
State law changes, net of federal income tax effect	59			(27		)
Increase deferred tax liability for organizational restructuring	(13		)	—
Increase deferred tax liability for business activity changes	—			(65		)
Credit for increasing research activities	11			8
Change in federal and state valuation allowance	11			(60		)
Other, net	(5		)	(16		)
Income tax expense	$	(64	)	$	(390	)
Effective income tax rate	14.4		%	71.2		%