Significant Accounting Policies (Health Plan Services Revenue Recognition) (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014	Jan. 01, 2013
Health Care Organizations [Line Items]
Accounts payable and other liabilities	$ 1,486,133,000		$ 1,486,133,000		$ 880,374,000
Other assets	309,543,000		309,543,000		220,122,000
Other noncurrent liabilities	277,922,000		277,922,000		242,705,000
Other noncurrent assets	270,097,000		270,097,000		187,630,000
Health plan services premiums	3,977,891,000	$ 3,631,617,000	11,702,123,000	$ 9,774,840,000
Commercial Premium Revenue [Member]
Health Care Organizations [Line Items]
Health plan services premiums	1,412,300,000	1,430,800,000	4,158,200,000	4,072,400,000
Medicaid Premium Revenue [Member]
Health Care Organizations [Line Items]
Health plan services premiums	1,668,100,000	1,397,700,000	4,812,500,000	3,381,600,000
Settlement account balance, beginning						$ 0
Settlement account payment, maximum			264,000,000
State Settlement Account Surplus	264,100,000		264,100,000		53,400,000
Medicare Premium Revenue [Member]
Health Care Organizations [Line Items]
Health plan services premiums	778,200,000	763,300,000	2,329,500,000	2,275,700,000
Medicare Risk adjustment [Member] | Medicare Premium Revenue [Member]
Health Care Organizations [Line Items]
Health plan services premiums	(1,400,000)	(5,500,000)	2,300,000	14,500,000
Medicaid Retro Premium Adjustment [Member] | Medicaid Premium Revenue [Member]
Health Care Organizations [Line Items]
Health plan services premiums	0	0	29,800,000	0
State-sponsored health plans settlement account deficit [Member] | Medicaid Premium Revenue [Member]
Health Care Organizations [Line Items]
Other noncurrent liabilities	0		0
Other noncurrent assets	0		0		0
Health plan services premiums	0	(9,600,000)	$ 0	(62,900,000)
Minimum [Member] | Medicaid Premium Revenue [Member]
Health Care Organizations [Line Items]
MLR Rebate Threshold			85.00%
Maximum [Member] | Medicaid Premium Revenue [Member]
Health Care Organizations [Line Items]
MLR Rebate Threshold			95.00%
MLR Rebate, Premium Refund [Member] | Commercial Premium Revenue [Member]
Health Care Organizations [Line Items]
Health plan services premiums	(400,000)	0	$ (400,000.0)	0
MLR Rebate, Premium Refund [Member] | Medicaid Premium Revenue [Member]
Health Care Organizations [Line Items]
Accounts payable and other liabilities	270,300,000		270,300,000		200,600,000
Health plan services premiums	(8,800,000)	(45,300,000)	(69,700,000)	(45,300,000)
Profit sharing, premium refund [Member] | Medicaid Premium Revenue [Member]
Health Care Organizations [Line Items]
Accounts payable and other liabilities	0		0		27,000,000
Other assets	1,300,000		1,300,000		0
Other noncurrent liabilities	34,100,000		34,100,000		0
Profit Corridor Payment			36,200,000
Other noncurrent assets	0		0		$ 2,300,000
Health plan services premiums	$ (18,500,000)	$ (3,900,000)	$ (44,300,000)	$ (11,900,000)