SHARE-BASED COMPENSATION PROGRAMS - SCHEDULE OF COMPENSATION COSTS (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation costs	$ 20.5	$ 10.1	$ 35.2	$ 45.1
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation costs	4.3	2.6	9.9	15.6
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation costs	0.6	0.4	1.1	1.1
Restricted Unit Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Adjustment for awards			10.9
Restricted Unit Awards | Alliance Bernstein
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation costs	14.9	5.6	22.4	26.9
Other compensation plans | Parent Company
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation costs	$ 0.7	$ 1.5	$ 1.8	$ 1.5