Fair Value Measurement (Tables)

9 Months Ended

12 Months Ended

Sep. 30, 2011

Dec. 31, 2010

Fair Value Measurement Abstract

Fair Value of Assets Measured on a Recurring Basis

Assets and liabilities measured at fair value on a recurring basis at September 30, 2011 are as follows:

	Fair value measurements						Total fair value
In millions	Level 1		Level 2		Level 3
Assets:
Cash and cash equivalents	$	1,403.8	$	—	$	—	$	1,403.8
Marketable securities	10.6		—		—		10.6
Derivative instruments	—		9.2		—		9.2
Benefit trust assets	15.3		153.0		—		168.3
Total	$	1,429.7	$	162.2	$	—	$	1,591.9
Liabilities:
Derivative instruments	$	—	$	43.7	$	—	$	43.7
Benefit trust liabilities	15.8		154.1		—		169.9
Total	$	15.8	$	197.8	$	—	$	213.6

Assets and liabilities measured at fair value on a recurring basis at December 31, 2010 are as follows:

	Fair value measurements						Total fair value
In millions	Level 1		Level 2		Level 3
Assets:
Cash and cash equivalents	$	1,014.3	$	—	$	—	$	1,014.3
Marketable securities	15.5		—		—		15.5
Derivative instruments	—		21.5		—		21.5
Benefit trust assets	17.3		155.2		—		172.5
Total	$	1,047.1	$	176.7	$	—	$	1,223.8
Liabilities:
Derivative instruments	$	—	$	2.6	$	—	$	2.6
Benefit trust liabilities	17.4		178.4		—		195.8
Total	$	17.4	$	181.0	$	—	$	198.4