Retirement Benefits - Fair values of pension plan assets by asset class (Details) - USD ($) $ in Thousands	12 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2018
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	$ 4,594,106	$ 4,244,969
Equity securities, U.S. based companies
Defined Benefit Plan Disclosure [Line Items]
Company stock included in U.S. based company equity securities	243,656	226,027
Fair Value, Inputs, Level 1, 2 and 3 | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	97,112	111,520
Fair Value, Inputs, Level 1, 2 and 3 | Equity securities, U.S. based companies
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	243,656	226,027
Fair Value, Inputs, Level 1, 2 and 3 | Equity securities, Non-U.S. based companies
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	9,152	16,385
Fair Value, Inputs, Level 1, 2 and 3 | Fixed income securities, Corporate debt securities
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	616,582	701,842
Fair Value, Inputs, Level 1, 2 and 3 | Fixed income securities, Government issued securities
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	471,059	528,394
Fair Value, Inputs, Level 1, 2 and 3 | Mutual funds, Equity funds
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	111,466	266,240
Fair Value, Inputs, Level 1, 2 and 3 | Mutual funds, Fixed income funds
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	12,912	183,732
Fair Value, Inputs, Level 1, 2 and 3 | Common/Collective trusts, Equity funds
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		84,790
Fair Value, Inputs, Level 1, 2 and 3 | Miscellaneous
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	(44,105)	(291,741)
Quoted Prices In Active Markets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	853,795	1,399,742
Quoted Prices In Active Markets (Level 1) | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	96,004	117,823
Quoted Prices In Active Markets (Level 1) | Equity securities, U.S. based companies
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	243,656	226,027
Quoted Prices In Active Markets (Level 1) | Equity securities, Non-U.S. based companies
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	9,152	16,385
Quoted Prices In Active Markets (Level 1) | Fixed income securities, Corporate debt securities
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	1,477	137,227
Quoted Prices In Active Markets (Level 1) | Fixed income securities, Government issued securities
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	379,128	367,518
Quoted Prices In Active Markets (Level 1) | Mutual funds, Equity funds
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	111,466	266,240
Quoted Prices In Active Markets (Level 1) | Mutual funds, Fixed income funds
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	12,912	183,732
Quoted Prices In Active Markets (Level 1) | Common/Collective trusts, Equity funds
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		84,790
Quoted Prices In Active Markets (Level 1) | Miscellaneous
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0	0
Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	664,039	427,447
Significant Other Observable Inputs (Level 2) | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	1,108	(6,303)
Significant Other Observable Inputs (Level 2) | Equity securities, U.S. based companies
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0	0
Significant Other Observable Inputs (Level 2) | Equity securities, Non-U.S. based companies
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0	0
Significant Other Observable Inputs (Level 2) | Fixed income securities, Corporate debt securities
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	615,105	564,615
Significant Other Observable Inputs (Level 2) | Fixed income securities, Government issued securities
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	91,931	160,876
Significant Other Observable Inputs (Level 2) | Mutual funds, Equity funds
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0	0
Significant Other Observable Inputs (Level 2) | Mutual funds, Fixed income funds
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0	0
Significant Other Observable Inputs (Level 2) | Common/Collective trusts, Equity funds
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		0
Significant Other Observable Inputs (Level 2) | Miscellaneous
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	(44,105)	(291,741)
Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0	0
Significant Unobservable Inputs (Level 3) | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0	0
Significant Unobservable Inputs (Level 3) | Equity securities, U.S. based companies
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0	0
Significant Unobservable Inputs (Level 3) | Equity securities, Non-U.S. based companies
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0	0
Significant Unobservable Inputs (Level 3) | Fixed income securities, Corporate debt securities
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0	0
Significant Unobservable Inputs (Level 3) | Fixed income securities, Government issued securities
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0	0
Significant Unobservable Inputs (Level 3) | Mutual funds, Equity funds
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0	0
Significant Unobservable Inputs (Level 3) | Mutual funds, Fixed income funds
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0	0
Significant Unobservable Inputs (Level 3) | Common/Collective trusts, Equity funds
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		0
Significant Unobservable Inputs (Level 3) | Miscellaneous
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0	0
Measured at Net Asset Value | Mutual funds measured at net asset value
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	259,776	304,504
Measured at Net Asset Value | Common/Collective trusts measured at net asset value
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	2,711,736	1,872,473
Measured at Net Asset Value | Limited Partnerships measured at net asset value
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	104,760	240,803
Pension Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	$ 4,594,106	$ 4,244,969	$ 3,915,889
Common/Collective trusts measured at net asset value
Defined Benefit Plan Disclosure [Line Items]
Investments valued using a net asset value per share, redemption notice period	90 days
Hedge Funds
Defined Benefit Plan Disclosure [Line Items]
Investments valued using a net asset value per share, redemption notice period	95 days
Limited Partnerships measured at net asset value
Defined Benefit Plan Disclosure [Line Items]
Investments valued using a net asset value per share, redemption notice period	90 days
Investments valued using a net asset value per share, redemption restriction period	2 years
Investments valued using a net asset value per share, redemption restriction	20.00%
Investments valued using a net asset value per share, redemption restriction, frequency period	6 months