Significant Accounting Policies (Health Care Services) (Details) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Health Care Organizations [Line Items]
Provision for adverse deviation	$ 53,000,000				$ 48,000,000				$ 53,000,000	$ 48,000,000
Health plan services costs	2,332,800,000	2,281,400,000	2,358,500,000	2,343,700,000	2,149,900,000	2,149,300,000	2,123,300,000	2,117,300,000	9,316,313,000	8,539,754,000	8,219,832,000
Premium deficiency reserve	9,400,000				900,000				9,400,000	900,000
Incurred claims from prior years [Member]
Health Care Organizations [Line Items]
Health plan services costs			$ 7,900,000	$ 25,000,000					$ 35,000,000	$ (97,000,000)