Stockholders' Equity (Other Comprehensive (Loss) Income) (Details) - USD ($) $ in Millions		12 Months Ended
		Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2017
Accumulated Other Comprehensive Income Loss [Line Items]
Other comprehensive (loss) income, net of tax		$ (89)	$ 140	$ 10
Benefit plan adjustments and other
Accumulated Other Comprehensive Income Loss [Line Items]
Unrealized (losses) gains, before tax		(133)	5	7
Reclassifications realized in net income, before tax	[1]	12	8	8
Other comprehensive (loss) income, before tax		(121)	13	15
Unrealized (losses) gains, tax		35	(1)	(2)
Reclassifications realized in net income, tax	[1]	(3)	(2)	(3)
Other comprehensive (loss) income, tax		32	(3)	(5)
Unrealized (losses) gains, net of tax		(98)	4	5
Reclassifications realized in net income, net of tax	[1]	9	6	5
Other comprehensive (loss) income, net of tax		$ (89)	10	$ 10
Gains on securities
Accumulated Other Comprehensive Income Loss [Line Items]
Unrealized (losses) gains, before tax			222
Other comprehensive (loss) income, before tax			222
Unrealized (losses) gains, tax			(92)
Other comprehensive (loss) income, tax			(92)
Unrealized (losses) gains, net of tax			130
Other comprehensive (loss) income, net of tax			$ 130

[1] Reclassifications of amounts related to benefit plan adjustments are included in Other, net in the Statements of Operations (See Note 14—Pension and Other Postretirement Benefits for additional information).