Retirement Benefits - Fair values of pension plan assets by asset class (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Jun. 30, 2020
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	$ 5,305,577	$ 4,594,106
Fair Value, Inputs, Level 1, 2 and 3 | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	248,525	97,112
Fair Value, Inputs, Level 1, 2 and 3 | Equity securities, U.S. based companies
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	408,301	243,656
Fair Value, Inputs, Level 1, 2 and 3 | Equity securities, Non-U.S. based companies
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	12,834	9,152
Fair Value, Inputs, Level 1, 2 and 3 | Fixed income securities, Corporate debt securities
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	531,497	616,582
Fair Value, Inputs, Level 1, 2 and 3 | Fixed income securities, Government issued securities
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	151,458	471,059
Fair Value, Inputs, Level 1, 2 and 3 | Mutual funds, Equity funds
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	6,768	111,466
Fair Value, Inputs, Level 1, 2 and 3 | Mutual funds, Fixed income funds
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	6,506	12,912
Fair Value, Inputs, Level 1, 2 and 3 | Miscellaneous
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	283,059	(44,105)
Quoted Prices In Active Markets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	782,437	853,795
Quoted Prices In Active Markets (Level 1) | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	241,421	96,004
Quoted Prices In Active Markets (Level 1) | Equity securities, U.S. based companies
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	408,301	243,656
Quoted Prices In Active Markets (Level 1) | Equity securities, Non-U.S. based companies
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	12,834	9,152
Quoted Prices In Active Markets (Level 1) | Fixed income securities, Corporate debt securities
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	1,440	1,477
Quoted Prices In Active Markets (Level 1) | Fixed income securities, Government issued securities
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	105,167	379,128
Quoted Prices In Active Markets (Level 1) | Mutual funds, Equity funds
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	6,768	111,466
Quoted Prices In Active Markets (Level 1) | Mutual funds, Fixed income funds
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	6,506	12,912
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	866,511	664,039
Significant Other Observable Inputs (Level 2) | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	7,104	1,108
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	530,057	615,105
Significant Other Observable Inputs (Level 2) | Fixed income securities, Government issued securities
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	46,291	91,931
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) | Miscellaneous
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	283,059	(44,105)
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) | 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	368,340	259,776
Measured at Net Asset Value | Common/Collective trusts measured at net asset value
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	3,161,683	2,711,736
Measured at Net Asset Value | Limited Partnerships measured at net asset value
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	$ 126,606	$ 104,760