Summary Of Significant Accounting Policies (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011 days years	Dec. 31, 2010	Dec. 31, 2009
Typical term (in years) of short-duration employer-group prepaid health services policies	1
Number of days notice for employer group to cancel short-duration prepaid health services policies	30
Depreciation and amortization expense	$ 33	$ 18	$ 13
Consumer discounts on brand name prescription drugs	50.00%
Building [Member]
Useful life, minimum years	20
Useful life, maximum years	40
Equipment [Member]
Useful life, maximum years	10
Computer Software [Member]
Useful life, minimum years	3
Useful life, maximum years	7
Securities Lending Program [Member]
Percentage of collateral to fair value of investment securities on loan	102.00%