Segment Information (Premium Revenue by Line of Business) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Segment Reporting Information [Line Items]
Health plan services premiums	$ 15,553,348	$ 13,361,170	$ 10,377,073
Commercial Premium Revenue [Member]
Segment Reporting Information [Line Items]
Health plan services premiums	5,530,500	5,443,100	5,175,400
Medicare Premium Revenue [Member]
Segment Reporting Information [Line Items]
Health plan services premiums	3,076,300	3,044,300	2,771,400
Medicaid Premium Revenue [Member]
Segment Reporting Information [Line Items]
Health plan services premiums	6,429,600	4,755,900	2,430,300
Dual eligibles premium revenue [Member]
Segment Reporting Information [Line Items]
Health plan services premiums	$ 516,900	$ 117,900	$ 0