Segment Information (Premium Revenue by Line of Business) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Segment Reporting Information [Line Items]
Health plan services premiums	$ 13,361,170	$ 10,377,073	$ 10,459,098
Commercial Premium Revenue [Member]
Segment Reporting Information [Line Items]
Health plan services premiums	5,443,100	5,175,400	5,705,500
Medicare Premium Revenue [Member]
Segment Reporting Information [Line Items]
Health plan services premiums	3,044,300	2,771,400	2,790,500
Medicaid Premium Revenue [Member]
Segment Reporting Information [Line Items]
Health plan services premiums	4,755,900	2,430,300	1,963,100
Dual eligibles premium revenue [Member]
Segment Reporting Information [Line Items]
Health plan services premiums	$ 117,900	$ 0	$ 0