Income Taxes (Tables)

3 Months Ended

Jun. 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 three-month periods endedJune 30, 2018 and 2017, respectively, were as follows:

	Three Months Ended June 30,
	2018			2017
	(in millions)
Income tax expense at the federal statutory rate	$	(46	)	$	(174	)
Effect of:
State income taxes, net of federal income tax effect	(15		)	(22		)
State law changes, net of federal income tax effect	24			3
Increase deferred tax liability for organizational restructuring	(13		)	—
Increase deferred tax liability for business activity changes	—			(65		)
Credit for increasing research activities	—			4
Change in federal and state valuation allowance	6			(33		)
Other, net	(3		)	(5		)
Income tax expense	$	(47	)	$	(292	)
Effective income tax rate	21.4		%	58.6		%

Schedule of Deferred Tax Assets and Liabilities