FAIR VALUE MEASUREMENT - Fair value hierarchy of financial instruments held (Details) - Fair Value, Nonrecurring - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Assets:
Deferred compensation plan assets	$ 35.8	$ 40.3
Note receivable - building sale		6.2
Total assets	1,578.3	116.5
Liabilities:
Deferred compensation plan liabilities	35.8	40.3
Debt	1,371.8	1,317.0
Total liabilities	1,407.6	1,357.3
US And UK Treasury securities
Assets:
Cash and cash equivalents	1,294.1
Money market funds
Assets:
Cash and cash equivalents	248.1
Level 1
Assets:
Deferred compensation plan assets	35.8	40.3
Note receivable - building sale		0.0
Total assets	1,578.3	110.3
Liabilities:
Deferred compensation plan liabilities	35.8	40.3
Debt	0.0	0.0
Total liabilities	35.8	40.3
Level 1 | US And UK Treasury securities
Assets:
Cash and cash equivalents	1,294.1
Level 1 | Money market funds
Assets:
Cash and cash equivalents	248.1
Level 2
Assets:
Deferred compensation plan assets	0.0	0.0
Note receivable - building sale		0.0
Total assets	0.0	0.0
Liabilities:
Deferred compensation plan liabilities	0.0	0.0
Debt	1,371.8	1,317.0
Total liabilities	1,371.8	1,317.0
Level 2 | US And UK Treasury securities
Assets:
Cash and cash equivalents	0.0
Level 2 | Money market funds
Assets:
Cash and cash equivalents	0.0
Level 3
Assets:
Deferred compensation plan assets	0.0	0.0
Note receivable - building sale		6.2
Total assets	0.0	6.2
Liabilities:
Deferred compensation plan liabilities	0.0	0.0
Debt	0.0	0.0
Total liabilities	0.0	0.0
Level 3 | US And UK Treasury securities
Assets:
Cash and cash equivalents	0.0
Level 3 | Money market funds
Assets:
Cash and cash equivalents	0.0
US Treasury Securities
Assets:
U.S. Treasury securities	0.3	70.0
US Treasury Securities | Level 1
Assets:
U.S. Treasury securities	0.3	70.0
US Treasury Securities | Level 2
Assets:
U.S. Treasury securities	0.0	0.0
US Treasury Securities | Level 3
Assets:
U.S. Treasury securities	$ 0.0	$ 0.0