FINANCIAL INSTRUMENTS - Available-for-Sale Debt Securities in a Continuous Unrealized Loss Position (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]
Unrealized losses less than 12 months, fair value	$ 627.4	$ 1,510.4
Unrealized losses less than 12 months, gross unrealized losses	(0.7)	(49.1)
Unrealized losses more than 12 months, fair value	3,033.2	3,538.3
Unrealized losses more than 12 months, gross unrealized losses	(99.8)	(149.4)
Total unrealized losses, fair value	3,660.6	5,048.7
Total unrealized losses, gross unrealized losses	(100.5)	(198.5)
U.S. treasuries
Debt Securities, Available-for-sale [Line Items]
Unrealized losses less than 12 months, fair value	458.8	731.7
Unrealized losses less than 12 months, gross unrealized losses	(0.4)	(26.0)
Unrealized losses more than 12 months, fair value	1,427.5	1,886.9
Unrealized losses more than 12 months, gross unrealized losses	(43.5)	(70.6)
Total unrealized losses, fair value	1,886.3	2,618.6
Total unrealized losses, gross unrealized losses	(43.9)	(96.6)
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Unrealized losses less than 12 months, fair value	54.0	631.4
Unrealized losses less than 12 months, gross unrealized losses	(0.1)	(17.6)
Unrealized losses more than 12 months, fair value	1,248.8	1,221.9
Unrealized losses more than 12 months, gross unrealized losses	(42.2)	(58.4)
Total unrealized losses, fair value	1,302.8	1,853.3
Total unrealized losses, gross unrealized losses	(42.3)	(76.0)
U.S. government agencies
Debt Securities, Available-for-sale [Line Items]
Unrealized losses less than 12 months, fair value	114.6	102.7
Unrealized losses less than 12 months, gross unrealized losses	(0.2)	(4.4)
Unrealized losses more than 12 months, fair value	274.6	324.6
Unrealized losses more than 12 months, gross unrealized losses	(11.0)	(15.5)
Total unrealized losses, fair value	389.2	427.3
Total unrealized losses, gross unrealized losses	(11.2)	(19.9)
Municipal securities
Debt Securities, Available-for-sale [Line Items]
Unrealized losses less than 12 months, fair value	0.0	44.6
Unrealized losses less than 12 months, gross unrealized losses	0.0	(1.1)
Unrealized losses more than 12 months, fair value	82.3	104.9
Unrealized losses more than 12 months, gross unrealized losses	(3.1)	(4.9)
Total unrealized losses, fair value	82.3	149.5
Total unrealized losses, gross unrealized losses	$ (3.1)	$ (6.0)