Reserve for Claims and Other Settlements (Details) - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Reserves for Claims and Other Settlements [Abstract]
Provision for adverse deviation		$ 74,300				$ 77,700				$ 74,300	$ 77,700	$ 53,400
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Reserve for claims, beginning of period	[1]				$ 1,186,300				$ 807,400	1,186,300	807,400	808,700
Incurred claims related to:
Current year	[2]									6,425,800	5,613,000	4,666,000
Liability for unpaid claims and claims adjustment expense, incurred claims, prior years	[3]									(107,400)	(14,600)	(56,200)
Total incurred	[4]									6,318,400	5,598,400	4,609,800
Paid claims related to:
Current year										5,321,000	4,443,200	3,872,500
Prior years										1,058,500	776,300	738,600
Total paid	[4]									6,379,500	5,219,500	4,611,100
Reserve for claims, end of period	[1]	1,125,200				1,186,300				1,125,200	1,186,300	807,400
Add:
Claims and claims-related payable	[5]	107,800				175,400				107,800	175,400	67,000
Other	[6]	260,400				534,300				260,400	534,300	109,700
Reserves for claims and other settlements		1,493,392				1,896,035				1,493,392	1,896,035	984,100
Prior Years Favorable Reserve Development										(29,700)
Health plan services, capitated and non-capitated expenses
Total incurred claims	[4]									6,318,400	5,598,400	4,609,800
Capitated expenses and shared risk										4,466,200	4,256,800	3,108,000
Pharmacy and other										2,256,400	1,452,600	1,168,700
Health plan services expenses		3,216,000	$ 3,318,400	$ 3,363,700	$ 3,142,900	3,038,200	$ 3,104,000	$ 2,763,200	$ 2,402,300	$ 13,041,036	$ 11,307,751	$ 8,886,547
Percentage of health plan services expense										52.00%	50.00%	48.00%
Prior Years Unfavorable Reserve Development											$ 36,600
Provision For Adverse Deviation, Release										$ (77,700)	(51,200)
Provision For Adverse Deviation		$ 74,300				$ 77,700				$ 74,300	$ 77,700

[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 $74.3 million, $77.7 million and $53.4 million as of December 31, 2015, 2014 and 2013, 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. For the year ended December 31, 2015, we had $107.4 million in favorable reserve developments related to prior years. This reserve development for the year ended December 31, 2015 consisted of $29.7 million in favorable prior year development and a release of $77.7 million of the provision for adverse deviation held at December 31, 2014. We believe that the $29.7 million favorable development for the year ended December 31, 2015 was primarily due to the growth of the new Medicaid expansion population in 2014. For the year ended December 31, 2014, we had $14.6 million in net favorable reserve developments related to prior years. This reserve development for the year ended December 31, 2014 consisted of $36.6 million in unfavorable prior year development primarily due to the existence of moderately adverse conditions and a release of $51.2 million of the provision for adverse deviation held at December 31, 2013. We believe that the $36.6 million unfavorable development for the year ended December 31, 2014 was 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. 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 do not directly correspond to an increase in our operating results 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. 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.