Acquisitions (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011
Number of states with Arcadian Medicare HMO members	15
MD Care [Member]
Date of acquisition	December 30, 2011
Anvita, Inc. [Member]
Date of acquisition	December 6, 2011
Amount allocated to other intangible assets	60
Goodwill acquired	117
Other intangible assets useful life, years	6.5
Concentra [Member]
Date of acquisition	December 21, 2010
Cash consideration	805.0
Accrual of payment of working capital adjustment to sellers	6
Total consideration paid including final working capital determination	811
Excess of consideration over estimated fair value of net tangible assets acquired	725
Amount allocated to other intangible assets	188
Goodwill acquired	537
Acquired goodwill deductible for tax purposes	58
Other intangible assets useful life, years	13.7