Fair Value Measurement (Details) (USD $) In Millions	Jun. 30, 2011	Dec. 31, 2010
Cash and cash equivalents	$ 1,259.8	$ 1,014.3
Marketable securities	13.5	15.5
Derivative instruments	11.5	21.5
Benefit trust assets	178.6	172.5
Total	1,463.4	1,223.8
Derivative instruments	7.5	2.6
Benefit trust liabilities	165.9	195.8
Total	173.4	198.4
Fair Value, Inputs, Level 1 [Member]
Cash and cash equivalents	1,259.8	1,014.3
Marketable securities	13.5	15.5
Derivative instruments	0	0
Benefit trust assets	19.9	17.3
Total	1,293.2	1,047.1
Derivative instruments	0	0
Benefit trust liabilities	16.0	17.4
Total	16.0	17.4
Fair Value, Inputs, Level 2 [Member]
Cash and cash equivalents	0	0
Marketable securities	0	0
Derivative instruments	11.5	21.5
Benefit trust assets	158.7	155.2
Total	170.2	176.7
Derivative instruments	7.5	2.6
Benefit trust liabilities	149.9	178.4
Total	157.4	181.0
Fair Value, Inputs, Level 3 [Member]
Cash and cash equivalents	0	0
Marketable securities	0	0
Derivative instruments	0	0
Benefit trust assets	0	0
Total	0	0
Derivative instruments	0	0
Benefit trust liabilities	0	0
Total	$ 0	$ 0