Fair Value Hierarchy (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011		Dec. 31, 2010
Estimate of Fair Value, Fair Value Disclosure
Fair value assets and liabilities measured on recurring and nonrecurring basis
Cash equivalents	$ 1,596.5		$ 1,744.4
Short-term marketable securities	12.9		13.7
Long-term investments	10.3		15.1
Assets, fair value disclosure, recurring	1,619.7		1,773.2
Fair value of assets measured on a recurring basis, percentage of total assets	12.60%		13.60%
Mandatorily redeemable noncontrolling interests	58.9	[1]	52.0	[1]
Fair Value, Inputs, Level 1
Fair value assets and liabilities measured on recurring and nonrecurring basis
Cash equivalents	1,596.5		1,744.4
Short-term marketable securities	12.9		13.7
Long-term investments	1.3		1.3
Assets, fair value disclosure, recurring	1,610.7		1,759.4
Fair value of assets measured on a recurring basis, percentage of total assets	12.50%		13.50%
Mandatorily redeemable noncontrolling interests	0	[1]	0	[1]
Fair Value, Inputs, Level 2
Fair value assets and liabilities measured on recurring and nonrecurring basis
Cash equivalents	0		0
Short-term marketable securities	0		0
Long-term investments	9.0		13.8
Assets, fair value disclosure, recurring	9.0		13.8
Fair value of assets measured on a recurring basis, percentage of total assets	0.10%		0.10%
Mandatorily redeemable noncontrolling interests	0	[1]	0	[1]
Fair Value, Inputs, Level 3
Fair value assets and liabilities measured on recurring and nonrecurring basis
Cash equivalents	0		0
Short-term marketable securities	0		0
Long-term investments	0		0
Assets, fair value disclosure, recurring	0		0
Fair value of assets measured on a recurring basis, percentage of total assets	0.00%		0.00%
Mandatorily redeemable noncontrolling interests	$ 58.9	[1]	$ 52.0	[1]

[1] Relates to unconditional obligations to purchase additional noncontrolling equity shares of consolidated subsidiaries. Fair value measurement of the obligation was based upon the amount payable as if the forward contracts were settled. The amount redeemable within the next twelve months is classified in accrued liabilities; any interests redeemable thereafter are classified in other non-current liabilities.