Equity (Summary of Changes in the Components of Accumulated Other Comprehensive (Loss) Income, Net of Tax) (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018		Dec. 31, 2017
Accumulated Other Comprehensive Income Loss [Line Items]
Balance, beginning of period		$ 11,054	$ 6,533	$ 9,594		$ 6,093
Other comprehensive income, net of tax		2	98	3		180
Transferred from 21CF investment		(642)	472	23		458
Balance, end of period		10,406	$ 7,953	10,406		$ 7,953
Unrealized holding gains on securities
Accumulated Other Comprehensive Income Loss [Line Items]
Balance, beginning of period		0		130
Adoption of ASUs		0		(130)	[1]
Other comprehensive income, net of tax		0		0
Transferred from 21CF investment		0		0
Balance, end of period		0		0
Benefit plan adjustments and other
Accumulated Other Comprehensive Income Loss [Line Items]
Balance, beginning of period		(61)		(49)
Adoption of ASUs		0		(13)	[2]
Other comprehensive income, net of tax		2		3
Transferred from 21CF investment	[3]	(143)		(143)
Balance, end of period		(202)		(202)
Accumulated other comprehensive (loss) income
Accumulated Other Comprehensive Income Loss [Line Items]
Balance, beginning of period		(61)		81
Adoption of ASUs		0		(143)
Other comprehensive income, net of tax		2		3
Transferred from 21CF investment		(143)		(143)
Balance, end of period		$ (202)		$ (202)

[1] Reflects the adoption of ASU 2016-01 (See Note 1 - Description of Business and Basis of Presentation under the heading “Recently Adopted and Recently Issued Accounting Guidance and U.S. Tax Reform” for additional information).

[2] Reflects the adoption of ASU 2018-02 (See Note 1 - Description of Business and Basis of Presentation under the heading “Recently Adopted and Recently Issued Accounting Guidance and U.S. Tax Reform” for additional information).

[3] See Note 10 - Pension and Other Postretirement Benefits.