EARNINGS AND DIVIDENDS PER SHARE (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions		3 Months Ended									12 Months Ended
	Jan. 19, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Jun. 30, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Earnings per share
Net income attributable to JCG											$ 155.8	$ 154.4	$ 114.7
Less: Allocation of earnings to participating restricted stock awards											5.5	5.1
Net income available to common shareholders											$ 150.3	$ 149.3	$ 114.7
Weighted-average common shares outstanding - basic											179.7	182.2	184.6
Diluted effect of:
2018 Convertible Notes											3.7	1.5
Stock warrants											2.5
Stock options, restricted stock and other											0.9	1.2	1.3
Weighted-average diluted common shares outstanding - diluted											186.8	184.9	185.9
Earnings per share:
Basic earnings per share (in dollars per share)		$ 0.25	$ 0.11	$ 0.24	$ 0.24	$ 0.25	$ 0.22	$ 0.19	$ 0.16		$ 0.84	$ 0.82	$ 0.62
Diluted earnings per share (in dollars per share)		0.25	$ 0.10	$ 0.23	$ 0.23	$ 0.24	$ 0.22	$ 0.19	$ 0.16		0.80	0.81	0.62
Dividends paid per share		$ 0.09								$ 0.07	$ 0.35	$ 0.31	$ 0.21
Cash dividend declared (in dollars per share)	$ 0.09
Employee stock options
Anti-dilutive securities that have not been included in the calculation of weighted average diluted shares outstanding
Number of anti-dilutive securities that have not been included in the calculation of weighted average diluted shares outstanding												1.5	7.0
Unvested nonparticipating restricted stock and price-vesting units.
Anti-dilutive securities that have not been included in the calculation of weighted average diluted shares outstanding
Number of anti-dilutive securities that have not been included in the calculation of weighted average diluted shares outstanding											0.2	0.4	1.2