Stockholders' Equity (Summary of Components of Accumulated Other Comprehensive (Loss) Income, Net of Tax) (Details) - USD ($) $ in Millions	Jun. 30, 2019		Jun. 30, 2018	Jun. 30, 2017
Equity [Abstract]
Unrealized holding gains on securities	$ 0	[1]	$ 130	$ 0
Benefit plan adjustments and other	(308)	[2]	(49)	(59)
Accumulated other comprehensive (loss) income, net of tax	$ (308)		$ 81	$ (59)

[1] The decrease in Unrealized holding gains on securities is a result of the adoption of ASU 2016-01 (See Note 2—Summary of Significant Accounting Policies under the heading “Recently Adopted and Recently Issued Accounting Guidance and U.S. Tax Reform” for additional information).

[2] The increase in the accumulated other comprehensive loss for Benefit plan adjustments and other includes a reclassification of $13 million as a result of the adoption of ASU 2018-02 (See Note 2—Summary of Significant Accounting Policies under the heading “Recently Adopted and Recently Issued Accounting Guidance and U.S. Tax Reform” for additional information) and $157 million related to the Shared Plans (as defined in Note 14—Pension and Other Postretirement Benefits”) allocable to the Company’s employees that was transferred to the Company.