Reclassifications from Accumulated Other Comprehensive Income (Loss) (AOCI) - Schedule of changes in AOCI by component, net of tax (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016
Changes in the balance of Accumulated Other Comprehensive Income
Balances, period start			$ 1,198.6	$ 1,104.9
Balances, period end	$ 1,336.8	$ 1,130.3	1,336.8	1,130.3
Cash flow hedging items
Changes in the balance of Accumulated Other Comprehensive Income
Balances, period start	5.8	(11.0)	(2.3)	(21.8)
Other comprehensive income (loss) before reclassifications	14.9	(0.6)	21.0	3.9
Amounts reclassified from AOCI	0.1	4.4	2.1	10.7
Net other comprehensive income (loss)	15.0	3.8	23.1	14.6
Balances, period end	20.8	(7.2)	20.8	(7.2)
Pension and other postretirement benefit plan items
Changes in the balance of Accumulated Other Comprehensive Income
Balances, period start	(296.9)	(326.9)	(299.0)	(344.3)
Other comprehensive income (loss) before reclassifications	0.0	0.0	0.0	11.4
Amounts reclassified from AOCI	2.5	5.7	4.6	11.7
Net other comprehensive income (loss)	2.5	5.7	4.6	23.1
Balances, period end	(294.4)	(321.2)	(294.4)	(321.2)
Unrealized losses on available-for- sale securities
Changes in the balance of Accumulated Other Comprehensive Income
Balances, period start	(0.3)	(0.3)	(0.3)	(0.3)
Other comprehensive income (loss) before reclassifications	0.0	0.0	0.0	0.0
Amounts reclassified from AOCI	0.0	0.0	0.0	0.0
Net other comprehensive income (loss)	0.0	0.0	0.0	0.0
Balances, period end	(0.3)	(0.3)	(0.3)	(0.3)
Foreign currency items
Changes in the balance of Accumulated Other Comprehensive Income
Balances, period start	(39.7)	(44.2)	(41.5)	(43.5)
Other comprehensive income (loss) before reclassifications	(1.5)	(4.0)	0.3	(4.7)
Amounts reclassified from AOCI	0.0	0.0	0.0	0.0
Net other comprehensive income (loss)	(1.5)	(4.0)	0.3	(4.7)
Balances, period end	(41.2)	(48.2)	(41.2)	(48.2)
Accumulated Other Comprehensive (Loss) Income
Changes in the balance of Accumulated Other Comprehensive Income
Balances, period start	(331.1)	(382.4)	(343.1)	(409.9)
Other comprehensive income (loss) before reclassifications	13.4	(4.6)	21.3	10.6
Amounts reclassified from AOCI	2.6	10.1	6.7	22.4
Net other comprehensive income (loss)	16.0	5.5	28.0	33.0
Balances, period end	$ (315.1)	$ (376.9)	$ (315.1)	$ (376.9)