Quarterly Financial Information (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended	12 Months Ended
Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Summary of the quarterly results of operations
Net sales	$ 2,026.2	$ 2,286.2	$ 2,423.7	$ 2,614.4	$ 2,576.7	$ 2,705.1	$ 2,616.8	$ 2,553.0	$ 9,350.5	$ 10,451.6	$ 9,223.8
Cost of sales	1,444.2	1,647.9	1,767.8	1,943.7	1,954.4	2,026.9	1,943.5	1,905.8	6,803.6	7,830.6	6,826.2
Gross profit	582.0	638.3	655.9	670.7	622.3	678.2	673.3	647.2
Net income	68.9	52.8	91.6	102.9	93.7	96.9	97.8	87.9	316.2	376.3	324.7
Net income attributable to Reliance	$ 68.6	$ 51.4	$ 90.2	$ 101.3	$ 92.3	$ 95.5	$ 96.5	$ 87.2	$ 311.5	$ 371.5	$ 321.6
Basic earnings per common share (in dollars per share)	$ 0.96	$ 0.70	$ 1.21	$ 1.31	$ 1.19	$ 1.23	$ 1.24	$ 1.13	$ 4.20	$ 4.78	$ 4.19
Diluted earnings per common share (in dollars per share)	$ 0.94	$ 0.69	$ 1.20	$ 1.30	$ 1.18	$ 1.21	$ 1.22	$ 1.11	$ 4.16	$ 4.73	$ 4.14

The aggregate costs related to goods produced and sold and services rendered by an entity during the reporting period. This excludes costs incurred during the reporting period related to financial services rendered and other revenue generating activities.

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