SEGMENT INFORMATION - Financial Information (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment information
Revenues	$ 1,461.0	$ 1,437.6	$ 1,348.5	$ 1,334.2	$ 1,464.5	$ 1,423.2	$ 1,397.2	$ 1,381.7	$ 5,581.3	$ 5,666.6	$ 5,474.7
Income (loss) before income taxes	167.4	164.2	193.8	213.0	363.8	343.0	263.1	245.1	738.4	1,215.0	1,062.5
Interest expense, net	141.6	140.0	143.5	143.9	144.7	136.8	133.6	127.2	569.0	542.3	455.4
Operating income (loss)	309.0	$ 304.2	$ 337.3	$ 356.9	508.5	$ 479.8	$ 396.7	$ 372.3	1,307.4	1,757.3	1,517.9
Depreciation and amortization									249.3	487.3	497.6
Stock compensation expense									54.8	80.8	75.1
Restructuring and other charges									118.1
Loss on extinguishment of debt									71.9
Less: Securitization funding costs									213.4	220.2	156.6
Less: Interest expense on deposits									225.6	165.7	125.1
Capital expenditures									142.3	199.8	225.4
Total assets	26,494.8				30,387.7				26,494.8	30,387.7
Epsilon
Segment information
Total assets					4,157.4					4,157.4
Continuing Operations
Segment information
Revenues									5,581.3	5,666.6	5,474.7
Income (loss) before income taxes									738.4	1,215.0	1,062.5
Interest expense, net									569.0	542.3	455.4
Operating income (loss)									1,307.4	1,757.3	1,517.9
Depreciation and amortization									176.1	193.6	187.9
Stock compensation expense									25.1	44.4	41.3
Strategic transaction costs									11.7
Restructuring and other charges									118.1
Loss on extinguishment of debt									71.9
Adjusted EBITDA									1,710.3	1,995.3	1,747.1
Less: Securitization funding costs									213.4	220.2	156.6
Less: Interest expense on deposits									225.6	165.7	125.1
Adjusted EBITDA, net									1,271.3	1,609.4	1,465.4
Capital expenditures									86.5	93.3	118.2
LoyaltyOne
Segment information
Restructuring and other charges									50.8
Card Services
Segment information
Restructuring and other charges									29.4
Operating segment | LoyaltyOne
Segment information
Revenues									1,033.1	1,068.4	1,303.5
Income (loss) before income taxes									103.1	153.8	161.6
Interest expense, net									2.3	5.6	5.4
Operating income (loss)									105.4	159.4	167.0
Strategic transaction costs									1.0
Restructuring and other charges									50.8
Adjusted EBITDA									244.5	254.2	256.7
Adjusted EBITDA, net									244.5	254.2	256.7
Total assets	2,338.0				2,200.2				2,338.0	2,200.2
Operating segment | LoyaltyOne | Continuing Operations
Segment information
Depreciation and amortization									80.1	84.8	81.7
Stock compensation expense									7.2	10.0	8.0
Capital expenditures									41.5	34.0	55.2
Operating segment | Card Services
Segment information
Revenues									4,547.8	4,597.6	4,170.6
Income (loss) before income taxes									991.7	1,381.6	1,235.7
Interest expense, net									439.0	385.9	281.7
Operating income (loss)									1,430.7	1,767.5	1,517.4
Restructuring and other charges									29.4
Adjusted EBITDA									1,558.7	1,881.9	1,626.6
Less: Securitization funding costs									213.4	220.2	156.6
Less: Interest expense on deposits									225.6	165.7	125.1
Adjusted EBITDA, net									1,119.7	1,496.0	1,344.9
Total assets	23,931.1				23,904.2				23,931.1	23,904.2
Operating segment | Card Services | Continuing Operations
Segment information
Depreciation and amortization									89.3	101.1	98.4
Stock compensation expense									9.3	13.3	10.8
Capital expenditures									44.2	53.8	54.2
Corporate/Other
Segment information
Revenues									0.4	0.6	0.6
Income (loss) before income taxes									(356.4)	(320.4)	(334.8)
Interest expense, net									127.7	150.8	168.3
Operating income (loss)									(228.7)	(169.6)	(166.5)
Strategic transaction costs									10.7
Restructuring and other charges									37.9
Loss on extinguishment of debt									71.9
Adjusted EBITDA									(92.9)	(140.8)	(136.2)
Adjusted EBITDA, net									(92.9)	(140.8)	(136.2)
Total assets	$ 225.7				$ 125.9				225.7	125.9
Corporate/Other | Continuing Operations
Segment information
Depreciation and amortization									6.7	7.7	7.8
Stock compensation expense									8.6	21.1	22.5
Capital expenditures									$ 0.8	$ 5.5	$ 8.8