Reserve for Claims and Other Settlements (Details) (USD $)	3 Months Ended												12 Months Ended
	Dec. 31, 2012		Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012		Dec. 31, 2011		Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011		Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Reserve for claims, beginning of period					$ 720,800,000	[1]					$ 727,500,000	[1]	$ 720,800,000	[1]	$ 727,500,000	[1]	$ 692,200,000	[1]
Incurred claims related to:
Current year													4,950,900,000		4,733,000,000		4,644,200,000
Prior years													34,500,000	[2]	(96,500,000)	[2]	(70,000,000)	[2]
Total incurred													4,985,400,000	[3]	4,636,500,000	[3]	4,574,200,000	[3]
Paid claims related to: [Abstract]
Current year													4,156,600,000		4,024,400,000		3,929,300,000
Prior years													740,900,000		618,800,000		609,600,000
Total paid													4,897,500,000	[3]	4,643,200,000	[3]	4,538,900,000	[3]
Reserve for claims, end of period	808,700,000	[1]					720,800,000	[1]					808,700,000	[1]	720,800,000	[1]	727,500,000	[1]
Add:
Claims and claims-related payable	91,600,000	[4]					111,000,000	[4]					91,600,000	[4]	111,000,000	[4]	123,600,000	[4]
Other	137,700,000	[5]					80,300,000	[5]					137,700,000	[5]	80,300,000	[5]	90,900,000	[5]
Reserves for claims and other settlements	1,037,973,000						912,126,000						1,037,973,000		912,126,000		942,000,000
Health plan services, capitated and non-capitated expenses [Abstract]
Total incurred claims													4,985,400,000	[3]	4,636,500,000	[3]	4,574,200,000	[3]
Capitated expenses and shared risk													3,128,100,000		2,789,200,000		2,699,300,000
Pharmacy and other													1,202,800,000		1,114,100,000		946,300,000
Health plan services	$ 2,332,800,000		$ 2,281,400,000	$ 2,358,500,000	$ 2,343,700,000		$ 2,149,900,000		$ 2,149,300,000	$ 2,123,300,000	$ 2,117,300,000		$ 9,316,313,000		$ 8,539,754,000		$ 8,219,832,000
Percentage of health plan services expense													46.00%		46.00%		44.00%

[1] Consists of IBNR claims and received but unprocessed claims and reserves for loss adjustment expenses.

[2] This line represents the change in reserves attributable to the difference between the original estimate of incurred claims for prior years and the revised estimate. In developing the revised estimate, there were no changes in the approach used to determine the key actuarial assumptions, which are the completion factor and medical cost trend. Claims liabilities were estimated under GAAP and actuarial standards of practice. The majority of the reserve balance held at each quarter-end is associated with the most recent months’ incurred services because these were the services for which the fewest claims have been paid. The degree of uncertainty in the estimates of incurred claims was greater for the most recent months’ incurred services. Revised estimates for prior years were determined in each quarter based on the most recent updates of paid claims for prior years. As of December 31, 2012, 2011 and 2010, incurred claims related to prior years were estimated to be $34.5 million higher, $96.5 million lower and $70.0 million lower, respectively, than originally estimated. The majority of these amounts were due to adjustments to our reserves that related to variables and uncertainties associated with our assumptions. As our reserve balance for older months of service decreased, and estimates of our incurred costs for older dates of service became more certain and predictable, our estimates of incurred claims related to prior periods were adjusted accordingly. The change in prior years incurred claims was favorable in 2011 and unfavorable in 2012. We believe this unfavorable reserve development in 2012 was primarily due to significant delays in claims submissions for the fourth quarter of 2011 arising from issues related to a new billing format required by HIPAA coupled with an unanticipated flattening of commercial trends and higher commercial large group claims trend. See Note 2 under the heading "Health Plan Services Health Care Cost" for more information.

[3] Includes medical claims only. Capitation, pharmacy and other payments (including, for example, provider settlements) are not included.

[4] Includes claims payable, provider dispute reserve, and other claims-related liabilities.

[5] Includes accrued capitation, shared risk settlements, and other reserve items.