Debt - HealthSpring Acquisition (Details) (HealthSpring [Member], USD $) In Millions, unless otherwise specified	Jan. 31, 2012
HealthSpring [Member]
Business Acquisition [Line Items]
HealthSpring debt at acquisition date	$ 326

The amount of acquisition cost of a business combination allocated to the current portion of long-term debt of the acquired entity.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 141

-Paragraph 51

-Subparagraph e

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Name:	us-gaap_BusinessAcquisitionPurchasePriceAllocationCurrentLiabilitiesLongTermDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant