STOCKHOLDERS' EQUITY - Capital Stock (Details) - At-The-Market Equity Offering Program $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2021 USD ($) $ / shares shares	Sep. 30, 2021 USD ($) $ / shares shares
Equity offering [Line Items]
Equity offering program, remaining authorized offering amount	$ 129.0	$ 129.0
Stock issued during period, shares, new issues, equity offering program | shares	10.6	10.9
Issuance of common stock	$ 611.7	$ 626.4
Shares Issued, Price Per Share | $ / shares	$ 57.73	$ 57.71