Segment and Related Information (Details) (USD $) In Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Segment information
Revenue	$ 1,580.8	$ 1,474.1	$ 2,862.7	$ 2,664.4
Operating Income (Loss)	358.8	326.3	573.2	516.5
S&P [Member]
Segment information
Revenue	480.3	405.0	923.2	806.3
Operating Income (Loss)	212.7	181.4	403.1	370.2
MH Financial [Member]
Segment information
Revenue	333.4	293.6	657.4	572.5
Operating Income (Loss)	97.8	83.4	194.1	154.6
MHE [Member]
Segment information
Revenue	536.6	565.1	839.3	882.2
Operating Income (Loss)	42.2	51.6	(33.3)	(10.2)
I&M [Member]
Segment information
Revenue	246.0	224.2	473.5	430.4
Operating Income (Loss)	50.3	47.5	87.7	75.3
Intersegment Elimination [Member]
Segment information
Revenue	(15.5)	(13.8)	(30.7)	(27.0)
Total operating segments [Member]
Segment information
Revenue	1,580.8	1,474.1	2,862.7	2,664.4
Operating Income (Loss)	403.0	363.9	651.6	589.9
General corporate expense [Member]
Segment information
Operating Income (Loss)	$ (44.2)	$ (37.6)	$ (78.4)	$ (73.4)