Segment Information (Premium Revenue by Line of Business) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Segment Reporting Information [Line Items]
Health plans services premiums	$ 10,459,098	$ 9,878,687	$ 9,492,460
Western Region Operations [Member]
Segment Reporting Information [Line Items]
Health plans services premiums	10,459,100	9,876,300	9,421,300
Commercial Premium Revenue [Member]
Segment Reporting Information [Line Items]
Health plans services premiums	5,705,500	5,945,900	5,663,900
Medicare Premium Revenue [Member]
Segment Reporting Information [Line Items]
Health plans services premiums	2,790,500	2,437,100	2,524,100
Medicaid Premium Revenue [Member]
Segment Reporting Information [Line Items]
Health plans services premiums	1,963,100	1,493,300	1,233,300
Divested Operations and Services [Member]
Segment Reporting Information [Line Items]
Health plans services premiums	$ 0	$ 2,400	$ 71,200