Stockholders' Equity (Other Comprehensive (Loss) Income) (Details) - USD ($) $ in Millions		12 Months Ended
		Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2018
Accumulated Other Comprehensive Income Loss [Line Items]
Other comprehensive (loss) income, net of tax		$ (109)	$ (89)	$ 140
Benefit plan adjustments and other
Accumulated Other Comprehensive Income Loss [Line Items]
Unrealized (losses) gains, before tax		(175)	(133)	5
Reclassifications realized in net income, before tax	[1]	29	12	8
Other comprehensive (loss) income, before tax		(146)	(121)	13
Unrealized (losses) gains, tax		44	35	(1)
Reclassifications realized in net income, tax	[1]	(7)	(3)	(2)
Other comprehensive (loss) income, tax		37	32	(3)
Unrealized (losses) gains, net of tax		(131)	(98)	4
Reclassifications realized in net income, net of tax	[1]	22	9	6
Other comprehensive (loss) income, net of tax		$ (109)	$ (89)	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 15—Pension and Other Postretirement Benefits for additional information).