RETIREMENT-RELATED BENEFITS - Net Periodic Benefit Cost of Retirement-Related Benefit Plans (Details) - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2022	Jun. 30, 2021
Defined Benefit Pension Plans
Cost/(Income) of Pension Plans
Service cost	$ 12.0	$ 23.0
Interest cost	$ 9.0	$ 2.0
Interest cost - income statement location	Other expense (income)	Other expense (income)
Expected return on plan assets	$ (11.0)	$ (6.0)
Expected return on plan assets - income statement location	Other expense (income)	Other expense (income)
Recognized actuarial losses (gains)	$ 10.0	$ 10.0
Recognized actuarial losses - income statement location	Other expense (income)	Other expense (income)
Multi-employer plans/other costs	$ 1.0	$ 2.0
Net periodic benefit cost	$ 22.0	31.0
Non Pension Postretirement Benefit Plans
Cost/(Income) of Pension Plans
Service cost		$ 1.0
Interest cost - income statement location	Other expense (income)	Other expense (income)
Expected return on plan assets - income statement location	Other expense (income)	Other expense (income)
Recognized actuarial losses - income statement location	Other expense (income)	Other expense (income)
Net periodic benefit cost		$ 1.0