Earnings Per Share (“EPS”) - Schedule of Reconciliation of Income from Continuing Operations and Computation of Earnings per Share (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Earnings Per Share [Abstract]
Income (loss) from continuing operations	$ 3.2	$ (50.8)	$ 4.9	$ (42.6)
Exclude: (Income) loss attributable to noncontrolling interest	(0.2)	1.1	0.4	1.8
Income (loss) from continuing operations attributable to A&B shareholders	3.0	(49.7)	5.3	(40.8)
Distributions and allocations to participating securities	0.0	0.0	0.0	0.0
Income (loss) from continuing operations available to A&B common shareholders	3.0	(49.7)	5.3	(40.8)
Income (loss) from discontinued operations available to A&B common shareholders	0.0	(0.1)	(0.8)	(0.8)
Net income (loss) available to A&B common shareholders	$ 3.0	$ (49.8)	$ 4.5	$ (41.6)
Number of shares used to compute basic and diluted earnings per share [Abstract]
Denominator for basic EPS – weighted-average shares outstanding (in shares)	72.4	72.3	72.3	72.2
Effect of dilutive securities:
Non-participating stock options and restricted stock unit awards (in shares)	0.0	0.0	0.1	0.0
Denominator for diluted EPS – weighted average shares outstanding (in shares)	72.4	72.3	72.4	72.2