Goodwill and Other Intangible Assets - Goodwill and Accumulated Goodwill Impairment Losses (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Jun. 30, 2021
Goodwill [Line Items]
Goodwill, gross	$ 2,639.9	$ 2,648.4
Accumulated goodwill impairment losses	(1,482.8)	(1,482.8)
Goodwill, net	1,157.1	1,165.6
Goodwill acquired during the period	8.5
Operating Segments | Northeast
Goodwill [Line Items]
Goodwill, gross	914.3	914.3
Accumulated goodwill impairment losses	(761.4)	(761.4)
Goodwill, net	152.9	152.9
Goodwill acquired during the period	0.0
Operating Segments | South
Goodwill [Line Items]
Goodwill, gross	236.6	236.6
Accumulated goodwill impairment losses	(61.0)	(61.0)
Goodwill, net	175.6	175.6
Goodwill acquired during the period	0.0
Operating Segments | West
Goodwill [Line Items]
Goodwill, gross	216.8	216.8
Accumulated goodwill impairment losses	(16.6)	(16.6)
Goodwill, net	200.2	200.2
Goodwill acquired during the period	0.0
Operating Segments | Midwest
Goodwill [Line Items]
Goodwill, gross	1,116.7	1,116.7
Accumulated goodwill impairment losses	(556.1)	(556.1)
Goodwill, net	560.6	560.6
Goodwill acquired during the period	0.0
Other
Goodwill [Line Items]
Goodwill, gross	155.5	164.0
Accumulated goodwill impairment losses	(87.7)	(87.7)
Goodwill, net	67.8	$ 76.3
Goodwill acquired during the period	$ 8.5