Summary of Significant Accounting Policies (Taxes) (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Significant Accounting Policies [Line Items]
Health plan services premiums	$ 13,361,170,000	$ 10,377,073,000	$ 10,459,098,000
State Required Premium Income Taxes [Member]
Significant Accounting Policies [Line Items]
Premium taxes paid based on membership or billed premiums	191,200,000	124,400,000	51,600,000
Reinstated Medicaid premium tax [Member]
Significant Accounting Policies [Line Items]
Taxes, Other	157,100,000	92,800,000
Reinstated prior year Medicaid premium taxes [Member] [Member]
Significant Accounting Policies [Line Items]
Taxes, Other		20,200,000
Medicaid Premium Revenue [Member]
Significant Accounting Policies [Line Items]
Health plan services premiums	4,755,900,000	2,430,300,000	1,963,100,000
Medicaid Premium Revenue [Member] | Reinstated Medicaid premium tax [Member]
Significant Accounting Policies [Line Items]
Health plan services premiums	$ 157,100,000	$ 92,800,000