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RESTRUCTURING AND OTHER CHARGES - Liability (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2019
Restructuring Reserve
Charged to expense			$ 118.1
Adjustments for non-cash charges			(51.4)
Cash payments			(31.9)
Restructuring Reserve, Ending Balance	$ 34.8		34.8
LoyaltyOne
Restructuring Reserve
Charged to expense			50.8
Card Services
Restructuring Reserve
Charged to expense			29.4
Termination Benefits
Restructuring Reserve
Charged to expense			53.5
Cash payments			(18.8)
Restructuring Reserve, Ending Balance	34.7		34.7
Termination Benefits \| LoyaltyOne
Restructuring Reserve
Charged to expense		$ 8.1	7.6
Termination Benefits \| Card Services
Restructuring Reserve
Charged to expense	27.3		27.3
Asset Impairments
Restructuring Reserve
Charged to expense			52.0
Adjustments for non-cash charges			(52.0)
Asset Impairments \| LoyaltyOne
Restructuring Reserve
Charged to expense	2.6	33.5	40.7
Asset Impairments \| Card Services
Restructuring Reserve
Charged to expense		0.2	0.2
Lease Termination Costs
Restructuring Reserve
Charged to expense			9.1
Adjustments for non-cash charges			0.7
Cash payments			(9.8)
Lease Termination Costs \| LoyaltyOne
Restructuring Reserve
Charged to expense		$ 0.2	0.2
Lease Termination Costs \| Card Services
Restructuring Reserve
Charged to expense			1.9
Other Exit Costs
Restructuring Reserve
Charged to expense			3.5
Adjustments for non-cash charges			(0.1)
Cash payments			(3.3)
Restructuring Reserve, Ending Balance	$ 0.1		0.1
Other Exit Costs \| LoyaltyOne
Restructuring Reserve
Charged to expense			$ 2.3