Consolidated Statements Stockholders' Deficit - USD ($) shares in Millions, $ in Millions	Total	Common Stock	Additional Paid-in-Capital	Retained Earnings	Treasury Stock	Accumulated Other Comprehensive Income (Loss)	Total CDK Stockholders' Deficit	Non-controlling Interest
Stockholders' equity, beginning balance at Jun. 30, 2018	$ (347.3)	$ 1.6	$ 679.8	$ 753.0	$ (1,810.7)	$ 11.5	$ (364.8)	$ 17.5
Common stock, shares issued, beginning balance (in shares) at Jun. 30, 2018		160.3
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	183.2			179.3			179.3	3.9
Foreign currency translation adjustments	(18.1)					(18.1)	(18.1)
Stock-based compensation expense and related dividend equivalents	6.9		7.1	(0.2)			6.9
Common stock issued for the exercise and vesting of stock-based compensation awards, net	(13.8)		(30.1)		16.3		(13.8)
Dividends paid to stockholders	(38.0)			(38.0)			(38.0)
Repurchases of common stock	(374.1)		(52.0)		(322.1)		(374.1)
Dividend payments to noncontrolling owners	(8.2)							(8.2)
Common stock, shares issued, end balance (in shares) at Dec. 31, 2018		160.3
Stockholders' equity, ending balance at Dec. 31, 2018	(500.1)	$ 1.6	604.8	1,003.8	(2,116.5)	(7.0)	(513.3)	13.2
Stockholders' equity, beginning balance at Sep. 30, 2018	(299.6)	$ 1.6	654.6	933.6	(1,909.6)	5.1	(314.7)	15.1
Common stock, shares issued, beginning balance (in shares) at Sep. 30, 2018		160.3
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	90.9			89.0			89.0	1.9
Foreign currency translation adjustments	(12.1)					(12.1)	(12.1)
Stock-based compensation expense and related dividend equivalents	3.1		3.2	(0.1)			3.1
Common stock issued for the exercise and vesting of stock-based compensation awards, net	0.1		(1.0)		1.1		0.1
Dividends paid to stockholders	(18.7)			(18.7)			(18.7)
Repurchases of common stock	(260.0)		(52.0)		(208.0)		(260.0)
Dividend payments to noncontrolling owners	(3.8)							(3.8)
Common stock, shares issued, end balance (in shares) at Dec. 31, 2018		160.3
Stockholders' equity, ending balance at Dec. 31, 2018	(500.1)	$ 1.6	604.8	1,003.8	(2,116.5)	(7.0)	(513.3)	13.2
Stockholders' equity, beginning balance at Jun. 30, 2019	$ (714.5)	$ 1.6	688.5	911.6	(2,324.6)	(6.7)	(729.6)	15.1
Common stock, shares issued, beginning balance (in shares) at Jun. 30, 2019	160.3	160.3
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	$ 108.2			104.3			104.3	3.9
Foreign currency translation adjustments	12.1					12.1	12.1
Stock-based compensation expense and related dividend equivalents	11.1		11.4	(0.3)			11.1
Common stock issued for the exercise and vesting of stock-based compensation awards, net	(0.8)		(16.9)		16.1		(0.8)
Dividends paid to stockholders	(36.5)			(36.5)			(36.5)
Dividend payments to noncontrolling owners	$ (6.6)							(6.6)
Common stock, shares issued, end balance (in shares) at Dec. 31, 2019	160.3	160.3
Stockholders' equity, ending balance at Dec. 31, 2019	$ (627.0)	$ 1.6	683.0	979.1	(2,308.5)	5.4	(639.4)	12.4
Stockholders' equity, beginning balance at Sep. 30, 2019	(671.6)	$ 1.6	677.7	975.3	(2,312.4)	(26.6)	(684.4)	12.8
Common stock, shares issued, beginning balance (in shares) at Sep. 30, 2019		160.3
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	24.1			22.3			22.3	1.8
Foreign currency translation adjustments	32.0					32.0	32.0
Stock-based compensation expense and related dividend equivalents	7.3		7.5	(0.2)			7.3
Common stock issued for the exercise and vesting of stock-based compensation awards, net	1.7		(2.2)		3.9		1.7
Dividends paid to stockholders	(18.3)			(18.3)			(18.3)
Dividend payments to noncontrolling owners	$ (2.2)							(2.2)
Common stock, shares issued, end balance (in shares) at Dec. 31, 2019	160.3	160.3
Stockholders' equity, ending balance at Dec. 31, 2019	$ (627.0)	$ 1.6	$ 683.0	$ 979.1	$ (2,308.5)	$ 5.4	$ (639.4)	$ 12.4