Reserve for Claims and Other Settlements (Details) (USD $)	3 Months Ended												12 Months Ended
	Dec. 31, 2014		Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014		Dec. 31, 2013		Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013		Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Reserves for Claims and Other Settlements [Abstract]
Provision for adverse deviation	$ 77,700,000						$ 53,400,000						$ 77,700,000		$ 53,400,000
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Reserve for claims, beginning of period					807,400,000	[1]					808,700,000	[1]	807,400,000	[1]	808,700,000	[1]	720,800,000	[1]
Incurred claims related to:
Current year													5,613,000,000	[2]	4,666,000,000	[2]	4,950,900,000	[2]
Liability for unpaid claims and claims adjustment expense, incurred claims, prior years													(14,600,000)	[3]	(56,200,000)	[3]	34,500,000	[3]
Total incurred													5,598,400,000	[4]	4,609,800,000	[4]	4,985,400,000	[4]
Paid claims related to:
Current year													4,443,200,000		3,872,500,000		4,156,600,000
Prior years													776,300,000		738,600,000		740,900,000
Total paid													5,219,500,000	[4]	4,611,100,000	[4]	4,897,500,000	[4]
Reserve for claims, end of period	1,186,300,000	[1]					807,400,000	[1]					1,186,300,000	[1]	807,400,000	[1]	808,700,000	[1]
Add:
Claims and claims-related payable	175,400,000	[5]					67,000,000	[5]					175,400,000	[5]	67,000,000	[5]	91,600,000	[5]
Other	534,300,000	[6]					109,700,000	[6]					534,300,000	[6]	109,700,000	[6]	137,700,000	[6]
Reserves for claims and other settlements	1,896,035,000						984,075,000						1,896,035,000		984,075,000		1,038,000,000
Health plan services, capitated and non-capitated expenses
Total incurred claims													5,598,400,000	[4]	4,609,800,000	[4]	4,985,400,000	[4]
Capitated expenses and shared risk													4,256,800,000		3,108,000,000		3,128,100,000
Pharmacy and other													1,452,600,000		1,168,700,000		1,202,800,000
Health plan services expenses	3,038,200,000		3,104,000,000	2,763,200,000	2,402,300,000		2,229,300,000		2,196,600,000	2,191,900,000	2,268,700,000		11,307,751,000		8,886,547,000		9,316,313,000
Percentage of health plan services expense													50.00%		48.00%		46.00%
Prior Years Unfavorable Reserve Development													36,600,000
Provision For Adverse Deviation, Release													51,200,000
Provision For Adverse Deviation	$ 77,700,000						$ 53,400,000						$ 77,700,000		$ 53,400,000

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

[2] Our IBNR estimate also includes a provision for adverse deviation, which is an estimate for known environmental factors that are reasonably likely to affect the required level of IBNR reserves. Such amounts were $77.7 million, $53.4 million and $53.4 million as of December 31, 2014, 2013 and 2012, respectively; the increase in the provision for adverse deviation from December 31, 2013 to December 31, 2014 was primarily driven by growth in our new products offered or programs administered under the ACA.

[3] 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. Negative amounts in this line represent favorable development in estimated prior years’ health care costs. Positive amounts in this line represent unfavorable development in estimated prior years’ health care costs. The net favorable development related to prior years that was recorded in the year ended December 31, 2014 consisted of $36.6 million in unfavorable prior year development primarily due to unanticipated benefit utilization in our commercial business arising from dates of service in the fourth quarter of 2013 as a result of an uncertain environment related to the ACA and a release of $51.2 million of the provision for adverse deviation held at December 31, 2013. The favorable development related to prior years that was recorded in the year ended December 31, 2013 resulted from claims being settled for amounts less than originally estimated. In 2013, this was primarily due to the absence of moderately adverse conditions. The favorable developments related to prior years that were recorded in 2014 and 2013 do not directly correspond to an increase in our operating results for those periods because any favorable prior period reserve development increases current period net income only to the extent that the current period provision for adverse deviation (see footnote (f)) is less than the benefit recognized from the prior period favorable development. The unfavorable development in estimated prior years' health care costs for 2012 primarily resulted from significant delays in claims submissions for the fourth quarter of 2011 arising from issues related to a new billing format required by HIPAA combined with an unanticipated flattening of commercial trends. See Note 2 under the heading "Health Plan Services Health Care Cost" for more information.

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

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

[6] Includes accrued capitation, shared risk settlements, provider incentives and other reserve items.