Quarterly report pursuant to Section 13 or 15(d)

FAIR VALUE MEASUREMENTS - Fair Value, Assets and Liabilities Measured On Recurring Basis, Unobservable Input Reconciliation (Details)

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FAIR VALUE MEASUREMENTS - Fair Value, Assets and Liabilities Measured On Recurring Basis, Unobservable Input Reconciliation (Details) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2020
Jun. 30, 2019
Jun. 30, 2020
Jun. 30, 2019
Fair Value, Assets Measured On Recurring Basis, Unobservable Input Reconciliation [Roll Forward]        
Beginning balance $ 19.6 $ 106.7 $ 45.8 $ 91.4
Included in earnings 40.0 74.3 13.8 89.6
Settlements (24.3) (62.9) (24.3) (62.9)
Ending balance 35.3 118.1 35.3 118.1
Total gains for the period included in earnings attributable to the change in unrealized gains on assets still held at the reporting date 33.6 73.0 13.6 88.3
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]        
Beginning balance 0.0 (9.8) (1.1) 0.0
Included in earnings 0.0 4.5 (0.6) (5.3)
Settlements 0.0 5.3 1.7 5.3
Ending balance $ 0.0 $ 0.0 $ 0.0 $ 0.0