RETIREMENT-RELATED BENEFITS - Net Periodic Benefit Cost of Retirement-Related Benefit Plans (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Defined Benefit Pension Plans
Cost/(Income) of Pension Plans
Service cost	$ 12.0	$ 20.0	$ 24.0	$ 42.0
Interest cost	$ 9.0	$ 2.0	$ 18.0	$ 4.0
Interest cost - income statement location	Other expense (income)	Other expense (income)	Other expense (income)	Other expense (income)
Expected return on plan assets	$ (10.0)	$ (7.0)	$ (21.0)	$ (13.0)
Expected return on plan assets - income statement location	Other expense (income)	Other expense (income)	Other expense (income)	Other expense (income)
Recognized actuarial losses (gains)	$ 10.0	$ 12.0	$ 20.0	$ 21.0
Recognized actuarial losses - income statement location	Other expense (income)	Other expense (income)	Other expense (income)	Other expense (income)
Multi-employer plans/other costs	$ 3.0	$ 1.0	$ 4.0	$ 3.0
Net periodic benefit cost	$ 22.0	27.0	$ 44.0	57.0
Non Pension Postretirement Benefit Plans
Cost/(Income) of Pension Plans
Service cost		$ 1.0		$ 2.0
Interest cost - income statement location	Other expense (income)	Other expense (income)	Other expense (income)	Other expense (income)
Expected return on plan assets				$ (1.0)
Expected return on plan assets - income statement location	Other expense (income)	Other expense (income)	Other expense (income)	Other expense (income)
Recognized actuarial losses - income statement location	Other expense (income)	Other expense (income)	Other expense (income)	Other expense (income)
Net periodic benefit cost		$ 1.0		$ 1.0