Summary of Significant Accounting Policies Accounting for Certain Provisions of the ACA (Details) (USD $)	3 Months Ended								12 Months Ended			1 Months Ended
	Dec. 31, 2014 Customers	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014 Customers	Dec. 31, 2013	Dec. 31, 2012	Sep. 30, 2014
Supplementary Insurance Information, by Segment [Line Items]
Other assets	$ 220,122,000				$ 132,683,000				$ 220,122,000	$ 132,683,000
Other receivables	424,910,000				68,919,000				424,910,000	68,919,000
Accounts payable and other liabilities	880,374,000				397,036,000				880,374,000	397,036,000
Other noncurrent assets	187,630,000				162,551,000				187,630,000	162,551,000
Other noncurrent liabilities	242,705,000				213,427,000				242,705,000	213,427,000
Number of customers	6,000,000								6,000,000
Health plan services premiums									13,361,170,000	10,377,073,000	10,459,098,000
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
General and administrative expenses									1,552,364,000	1,083,694,000	939,940,000
Administrative services fees and other income									(1,725,000)	34,791,000	17,968,000
ACA Health Insurer Fee [Member]
Supplementary Insurance Information, by Segment [Line Items]
ACA Health Insurer Fee Payment									141,400,000			141,400,000
Amortization of deferred cost	35,400,000	31,900,000	37,800,000	36,300,000					141,400,000
Other assets	0								0
ACA Reinsurance Recovery [Member]
Supplementary Insurance Information, by Segment [Line Items]
Other receivables	234,000,000								234,000,000
Health plan services expenses									(234,000,000)
ACA Risk Adjustment [Member]
Supplementary Insurance Information, by Segment [Line Items]
Other receivables	81,000,000								81,000,000
Accounts payable and other liabilities	153,400,000								153,400,000
Health plan services premiums									(72,400,000)
ACA Risk Corridor [Member]
Supplementary Insurance Information, by Segment [Line Items]
Other noncurrent assets	90,400,000								90,400,000
Other noncurrent liabilities	3,600,000								3,600,000
Health plan services premiums									86,800,000
Full Risk [Member]
Supplementary Insurance Information, by Segment [Line Items]
Health plan services premiums			154,700,000
Health plan services expenses			144,000,000
General and administrative expenses			0
Administrative services fees and other income			(7,900,000)
Pretax income			2,800,000
No Risk [Member]
Supplementary Insurance Information, by Segment [Line Items]
Health plan services premiums				0						4,400,000
Health plan services expenses				0						0
General and administrative expenses				0						4,400,000
Administrative services fees and other income				1,400,000						6,500,000
Pretax income				1,400,000						6,500,000
Medicaid Premium Revenue [Member]
Supplementary Insurance Information, by Segment [Line Items]
Health plan services premiums									$ 4,755,900,000	$ 2,430,300,000	$ 1,963,100,000
Medicaid Premium Revenue [Member] | CALIFORNIA
Supplementary Insurance Information, by Segment [Line Items]
Number of customers	1,600,000								1,600,000
Medicaid Premium Revenue [Member] | ARIZONA
Supplementary Insurance Information, by Segment [Line Items]
Number of customers	81,000								81,000