Pension and Other Postretirement Benefits (Plan Assets and Grantor Trust Assets By Level) (Details) - USD ($) $ in Millions		Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2018
Grantor Trust
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		$ 247	$ 249
Grantor Trust Balanced Funds | Grantor Trust
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[1]	214	213
Grantor Trust Partnership Interest | Grantor Trust
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		13	15
Other | Grantor Trust
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[2]	20	21
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		788	800	$ 70
Pension Benefits | Money market funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[1]	33	83
Pension Benefits | Domestic equity funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[1]	73	72
Pension Benefits | Domestic fixed income funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[1]	3
Pension Benefits | International equity funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[1]	119	132
Pension Benefits | International fixed income funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[1]	29	39
Pension Benefits | Balanced Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[1]	181	198
Pension Benefits | U.S. common stocks
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[3]	144	131
Pension Benefits | Domestic government obligations
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[4]	19	17
Pension Benefits | Domestic agency obligations
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[4]	24	12
Pension Benefits | Corporate obligations
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[4]	50	44
Pension Benefits | Partnership interests
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		13	13
Pension Benefits | Exchange traded funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[3]	70	32
Pension Benefits | Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[2]	30	27
Level 1 | Grantor Trust
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		234	234
Level 1 | Grantor Trust Balanced Funds | Grantor Trust
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[1]	214	213
Level 1 | Grantor Trust Partnership Interest | Grantor Trust
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Level 1 | Other | Grantor Trust
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[2]	20	21
Level 1 | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		514	500
Level 1 | Pension Benefits | Money market funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[1]	0	0
Level 1 | Pension Benefits | Domestic equity funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[1]	73	72
Level 1 | Pension Benefits | Domestic fixed income funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[1]	3
Level 1 | Pension Benefits | International equity funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[1]	119	132
Level 1 | Pension Benefits | International fixed income funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[1]	1	0
Level 1 | Pension Benefits | Balanced Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[1]	114	136
Level 1 | Pension Benefits | U.S. common stocks
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[3]	144	131
Level 1 | Pension Benefits | Domestic government obligations
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[4]	0	0
Level 1 | Pension Benefits | Domestic agency obligations
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[4]	0	0
Level 1 | Pension Benefits | Corporate obligations
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[4]	0	0
Level 1 | Pension Benefits | Partnership interests
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Level 1 | Pension Benefits | Exchange traded funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[3]	70	32
Level 1 | Pension Benefits | Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[2]	(10)	(3)
Level 2 | Grantor Trust
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Level 2 | Grantor Trust Balanced Funds | Grantor Trust
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[1]	0	0
Level 2 | Grantor Trust Partnership Interest | Grantor Trust
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Level 2 | Other | Grantor Trust
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[2]	0	0
Level 2 | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		166	186
Level 2 | Pension Benefits | Money market funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[1]	33	83
Level 2 | Pension Benefits | Domestic equity funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[1]	0	0
Level 2 | Pension Benefits | Domestic fixed income funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[1]	0
Level 2 | Pension Benefits | International equity funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[1]	0	0
Level 2 | Pension Benefits | International fixed income funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[1]	0	0
Level 2 | Pension Benefits | Balanced Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[1]	0	0
Level 2 | Pension Benefits | U.S. common stocks
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[3]	0	0
Level 2 | Pension Benefits | Domestic government obligations
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[4]	19	17
Level 2 | Pension Benefits | Domestic agency obligations
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[4]	24	12
Level 2 | Pension Benefits | Corporate obligations
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[4]	50	44
Level 2 | Pension Benefits | Partnership interests
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Level 2 | Pension Benefits | Exchange traded funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[3]	0	0
Level 2 | Pension Benefits | Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[2]	40	30
Fair Value Measured at Net Asset Value Per Share | Grantor Trust
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[5]	13	15
Fair Value Measured at Net Asset Value Per Share | Grantor Trust Balanced Funds | Grantor Trust
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[1],[5]	0	0
Fair Value Measured at Net Asset Value Per Share | Grantor Trust Partnership Interest | Grantor Trust
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[5]	13	15
Fair Value Measured at Net Asset Value Per Share | Other | Grantor Trust
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[2],[5]	0	0
Fair Value Measured at Net Asset Value Per Share | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[5]	108	114
Fair Value Measured at Net Asset Value Per Share | Pension Benefits | Money market funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[1],[5]	0	0
Fair Value Measured at Net Asset Value Per Share | Pension Benefits | Domestic equity funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[1],[5]	0	0
Fair Value Measured at Net Asset Value Per Share | Pension Benefits | Domestic fixed income funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[1],[5]	0
Fair Value Measured at Net Asset Value Per Share | Pension Benefits | International equity funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[1],[5]	0	0
Fair Value Measured at Net Asset Value Per Share | Pension Benefits | International fixed income funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[1],[5]	28	39
Fair Value Measured at Net Asset Value Per Share | Pension Benefits | Balanced Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[1],[5]	67	62
Fair Value Measured at Net Asset Value Per Share | Pension Benefits | U.S. common stocks
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[3],[5]	0	0
Fair Value Measured at Net Asset Value Per Share | Pension Benefits | Domestic government obligations
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[4],[5]	0	0
Fair Value Measured at Net Asset Value Per Share | Pension Benefits | Domestic agency obligations
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[4],[5]	0	0
Fair Value Measured at Net Asset Value Per Share | Pension Benefits | Corporate obligations
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[4],[5]	0	0
Fair Value Measured at Net Asset Value Per Share | Pension Benefits | Partnership interests
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[5]	13	13
Fair Value Measured at Net Asset Value Per Share | Pension Benefits | Exchange traded funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[3],[5]	0	0
Fair Value Measured at Net Asset Value Per Share | Pension Benefits | Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[2],[5]	$ 0	$ 0

[1] Open-ended pooled funds that are registered and/or available to the general public are valued at the daily published NAV.

[2] Includes cash and cash equivalents, plan receivables and payables and certain other fixed income investments.

[3] Common stock investments that are publicly traded and exchange traded funds are valued at the closing price reported on active markets in which the securities are traded.

[4] The fair value of corporate, government and agency obligations are valued based on a compilation of primary observable market information or a broker quote in a non-active market.

[5] As a practical expedient, pooled funds are valued at the net asset value (“NAV”) provided by the fund issuer and partnership interests are based on the fair value obtained from the general partner.