Significant Accounting Policies (Health Plan Services Revenue Recognition) (Details) (USD $)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013	Dec. 31, 2012
Health Care Organizations [Line Items]
Health plans services premiums	$ 2,881,345,000	$ 2,632,069,000
Medicare Premium Revenue [Member]
Health Care Organizations [Line Items]
Health plans services premiums	755,200,000	706,400,000
Medicaid Premium Revenue [Member]
Health Care Organizations [Line Items]
Health plans services premiums	862,000,000	600,300,000
Settlement account balance, beginning				0
Settlement account payment, maximum	264,000,000
Settlement account payment, current balance	50,000,000		62,900,000
Receivable with imputed interest, discount	3,400,000		4,400,000
Settlement account payment premium revenue	(12,900,000)	20,800,000
Medicare Risk adjustment [Member] | Medicare Premium Revenue [Member]
Health Care Organizations [Line Items]
Health plans services premiums	15,600,000
Medicaid Retro Rate Adjustment [Member] | Medicaid Premium Revenue [Member]
Health Care Organizations [Line Items]
Health plans services premiums		$ 42,200,000